CLN: ASV io_bench, parser_vb
There are a lot of io benchmarks scattered among `hdfstore_bench.py`, `io_bench.py`, `parser_vb.py`, and `packer.py`. I think it would be a lot cleaner if each io method had it's own file (like `io_sql.py` which already exists)

This PR creates `io_csv.py` and `io_json.py` that consolidates the csv and json benchmarks that exist. Benchmarks were flake8'd, `param`'d, and simplified where available:

```
$ asv dev -b ^io_json
· Discovering benchmarks
· Running 15 total benchmarks (1 commits * 1 environments * 15 benchmarks)
[  0.00%] ·· Building for existing-py_home_matt_anaconda_envs_pandas_dev_bin_python
[  0.00%] ·· Benchmarking existing-py_home_matt_anaconda_envs_pandas_dev_bin_python
[  6.67%] ··· Running io_json.ReadJSON.time_read_json                                                              ok
[  6.67%] ···· 
               ========= ======= ==========
               --              index       
               --------- ------------------
                 orient    int    datetime 
               ========= ======= ==========
                 split    294ms    272ms   
                 index    7.61s    7.65s   
                records   614ms    613ms   
               ========= ======= ==========

[ 13.33%] ··· Running io_json.ReadJSONLines.peakmem_read_json_lines                                                ok
[ 13.33%] ···· 
               ========== ======
                 index          
               ---------- ------
                  int      192M 
                datetime   192M 
               ========== ======

[ 20.00%] ··· Running io_json.ReadJSONLines.peakmem_read_json_lines_concat                                         ok
[ 20.00%] ···· 
               ========== ======
                 index          
               ---------- ------
                  int      164M 
                datetime   164M 
               ========== ======

[ 26.67%] ··· Running io_json.ReadJSONLines.time_read_json_lines                                                   ok
[ 26.67%] ···· 
               ========== =======
                 index           
               ---------- -------
                  int      755ms 
                datetime   720ms 
               ========== =======

[ 33.33%] ··· Running io_json.ReadJSONLines.time_read_json_lines_concat                                            ok
[ 33.33%] ···· 
               ========== =======
                 index           
               ---------- -------
                  int      749ms 
                datetime   752ms 
               ========== =======

[ 40.00%] ··· Running io_json.ToJSON.time_delta_int_tstamp                                                         ok
[ 40.00%] ···· 
               ========= =======
                 orient         
               --------- -------
                 split    238ms 
                columns   234ms 
                 index    397ms 
               ========= =======

[ 46.67%] ··· Running io_json.ToJSON.time_delta_int_tstamp_lines                                                   ok
[ 46.67%] ···· 
               ========= =======
                 orient         
               --------- -------
                 split    593ms 
                columns   566ms 
                 index    540ms 
               ========= =======

[ 53.33%] ··· Running io_json.ToJSON.time_float_int                                                                ok
[ 53.33%] ···· 
               ========= =======
                 orient         
               --------- -------
                 split    237ms 
                columns   214ms 
                 index    371ms 
               ========= =======

[ 60.00%] ··· Running io_json.ToJSON.time_float_int_lines                                                          ok
[ 60.00%] ···· 
               ========= =======
                 orient         
               --------- -------
                 split    569ms 
                columns   570ms 
                 index    570ms 
               ========= =======

[ 66.67%] ··· Running io_json.ToJSON.time_float_int_str                                                            ok
[ 66.67%] ···· 
               ========= =======
                 orient         
               --------- -------
                 split    238ms 
                columns   216ms 
                 index    384ms 
               ========= =======

[ 73.33%] ··· Running io_json.ToJSON.time_float_int_str_lines                                                      ok
[ 73.33%] ···· 
               ========= =======
                 orient         
               --------- -------
                 split    598ms 
                columns   614ms 
                 index    617ms 
               ========= =======

[ 80.00%] ··· Running io_json.ToJSON.time_floats_with_dt_index                                                     ok
[ 80.00%] ···· 
               ========= =======
                 orient         
               --------- -------
                 split    182ms 
                columns   209ms 
                 index    208ms 
               ========= =======

[ 86.67%] ··· Running io_json.ToJSON.time_floats_with_dt_index_lines                                               ok
[ 86.67%] ···· 
               ========= =======
                 orient         
               --------- -------
                 split    442ms 
                columns   444ms 
                 index    449ms 
               ========= =======

[ 93.33%] ··· Running io_json.ToJSON.time_floats_with_int_idex_lines                                               ok
[ 93.33%] ···· 
               ========= =======
                 orient         
               --------- -------
                 split    442ms 
                columns   442ms 
                 index    441ms 
               ========= =======

[100.00%] ··· Running io_json.ToJSON.time_floats_with_int_index                                                    ok
[100.00%] ···· 
               ========= =======
                 orient         
               --------- -------
                 split    159ms 
                columns   171ms 
                 index    182ms 
               ========= =======
```

```
asv dev -b ^io_csv
· Discovering benchmarks
· Running 16 total benchmarks (1 commits * 1 environments * 16 benchmarks)
[  0.00%] ·· Building for existing-py_home_matt_anaconda_envs_pandas_dev_bin_python
[  0.00%] ·· Benchmarking existing-py_home_matt_anaconda_envs_pandas_dev_bin_python
[  6.25%] ··· Running io_csv.ReadCSVCategorical.time_convert_direct                                            99.1ms
[ 12.50%] ··· Running io_csv.ReadCSVCategorical.time_convert_post                                               139ms
[ 18.75%] ··· Running io_csv.ReadCSVComment.time_comment                                                       60.7ms
[ 25.00%] ··· Running io_csv.ReadCSVDInferDatetimeFormat.time_read_csv                                             ok
[ 25.00%] ···· 
               ======================= ======== ========= ========
               --                                 format          
               ----------------------- ---------------------------
                infer_datetime_format   custom   iso8601    ymd   
               ======================= ======== ========= ========
                         True           23.0ms    4.65ms   4.77ms 
                        False           619ms     3.49ms   3.18ms 
               ======================= ======== ========= ========

[ 31.25%] ··· Running io_csv.ReadCSVFloatPrecision.time_read_csv                                                   ok
[ 31.25%] ···· 
               ===== ========== ========== ================ ========== ========== ================
               --                              decimal / float_precision                          
               ----- -----------------------------------------------------------------------------
                sep   . / None   . / high   . / round_trip   _ / None   _ / high   _ / round_trip 
               ===== ========== ========== ================ ========== ========== ================
                 ,     3.89ms     3.73ms        5.12ms        4.17ms     4.10ms        4.16ms     
                 ;     3.87ms     3.71ms        5.23ms        4.11ms     4.18ms        4.23ms     
               ===== ========== ========== ================ ========== ========== ================

[ 37.50%] ··· Running io_csv.ReadCSVFloatPrecision.time_read_csv_python_engine                                     ok
[ 37.50%] ···· 
               ===== ========== ========== ================ ========== ========== ================
               --                              decimal / float_precision                          
               ----- -----------------------------------------------------------------------------
                sep   . / None   . / high   . / round_trip   _ / None   _ / high   _ / round_trip 
               ===== ========== ========== ================ ========== ========== ================
                 ,     7.84ms     7.76ms        7.80ms        6.14ms     6.24ms        6.25ms     
                 ;     7.76ms     7.80ms        8.41ms        6.10ms     6.25ms        6.14ms     
               ===== ========== ========== ================ ========== ========== ================

[ 43.75%] ··· Running io_csv.ReadCSVParseDates.time_baseline                                                   2.85ms
[ 50.00%] ··· Running io_csv.ReadCSVParseDates.time_multiple_date                                              2.84ms
[ 56.25%] ··· Running io_csv.ReadCSVSkipRows.time_skipprows                                                        ok
[ 56.25%] ···· 
               ========== ========
                skiprows          
               ---------- --------
                  None     44.8ms 
                 10000     30.9ms 
               ========== ========

[ 62.50%] ··· Running io_csv.ReadCSVThousands.time_thousands                                                       ok
[ 62.50%] ···· 
               ===== ======== ========
               --        thousands    
               ----- -----------------
                sep    None      ,    
               ===== ======== ========
                 ,    38.5ms   37.0ms 
                 |    37.8ms   39.6ms 
               ===== ======== ========

[ 68.75%] ··· Running io_csv.ReadUint64Integers.time_read_uint64                                               8.99ms
[ 75.00%] ··· Running io_csv.ReadUint64Integers.time_read_uint64_na_values                                     13.2ms
[ 81.25%] ··· Running io_csv.ReadUint64Integers.time_read_uint64_neg_values                                    12.9ms
[ 87.50%] ··· Running io_csv.S3.time_read_csv_10_rows                                                              ok
[ 87.50%] ···· 
               ============= ======== =======
               --                 engine     
               ------------- ----------------
                compression   python     c   
               ============= ======== =======
                    None      6.41s    6.13s 
                    gzip      6.20s    6.60s 
                    bz2       35.1s     n/a  
               ============= ======== =======

[ 93.75%] ··· Running io_csv.ToCSV.time_frame                                                                      ok
[ 93.75%] ···· 
               ======= ========
                 kind          
               ------- --------
                 wide   84.4ms 
                 long   164ms  
                mixed   37.4ms 
               ======= ========
```
