CLN: ASV  index_object benchmark
- Remove star imports and flake8 checked

- Moved some index constructor benchmarks to `ctors.py` (probably should rename this file in the future)

- Moved some index indexing benchmarks to `indexing.py`

```
asv dev -b ^index_object
· Discovering benchmarks
· Running 32 total benchmarks (1 commits * 1 environments * 32 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
[  0.00%] ··· Setting up /home/matt/Projects/pandas-mroeschke/asv_bench/benchmarks/index_object.py:160
[  3.12%] ··· Running index_object.MultiIndexValues.time_datetime_level_values_copy                     30.1ms
[  6.25%] ··· Running index_object.MultiIndexValues.time_datetime_level_values_sliced                    544μs
[  9.38%] ··· Running index_object.Datetime.time_is_dates_only                                           357μs
[ 12.50%] ··· Running index_object.Duplicated.time_duplicated                                            228ms
[ 15.62%] ··· Running index_object.IndexAppend.time_append_int_list                                      285ms
[ 18.75%] ··· Running index_object.IndexAppend.time_append_obj_list                                      299ms
[ 21.88%] ··· Running index_object.IndexAppend.time_append_range_list                                    310ms
[ 25.00%] ··· Running index_object.Ops.time_add                                                             ok
[ 25.00%] ···· 
               ======= ========
                dtype          
               ------- --------
                float   6.22ms 
                 int    5.53ms 
               ======= ========

[ 28.12%] ··· Running index_object.Ops.time_divide                                                          ok
[ 28.12%] ···· 
               ======= ========
                dtype          
               ------- --------
                float   5.59ms 
                 int    20.7ms 
               ======= ========

[ 31.25%] ··· Running index_object.Ops.time_modulo                                                          ok
[ 31.25%] ···· 
               ======= ========
                dtype          
               ------- --------
                float   15.8ms 
                 int    19.1ms 
               ======= ========

[ 34.38%] ··· Running index_object.Ops.time_multiply                                                        ok
[ 34.38%] ···· 
               ======= ========
                dtype          
               ------- --------
                float   5.55ms 
                 int    5.82ms 
               ======= ========

[ 37.50%] ··· Running index_object.Ops.time_subtract                                                        ok
[ 37.50%] ···· 
               ======= ========
                dtype          
               ------- --------
                float   5.53ms 
                 int    5.51ms 
               ======= ========

[ 40.62%] ··· Running index_object.Range.time_max                                                       65.6ms
[ 43.75%] ··· Running index_object.Range.time_max_trivial                                               61.5ms
[ 46.88%] ··· Running index_object.Range.time_min                                                       62.4ms
[ 50.00%] ··· Running index_object.Range.time_min_trivial                                               63.3ms
[ 53.12%] ··· Running index_object.SetOperations.time_datetime_difference                               14.2ms
[ 56.25%] ··· Running index_object.SetOperations.time_datetime_difference_disjoint                      8.42ms
[ 59.38%] ··· Running index_object.SetOperations.time_datetime_intersection                             1.35ms
[ 62.50%] ··· Running index_object.SetOperations.time_datetime_symmetric_difference                     18.5ms
[ 65.62%] ··· Running index_object.SetOperations.time_datetime_union                                     895μs
[ 68.75%] ··· Running index_object.SetOperations.time_index_datetime_intersection                       6.96ms
[ 71.88%] ··· Running index_object.SetOperations.time_index_datetime_union                              6.91ms
[ 75.00%] ··· Running index_object.SetOperations.time_int64_difference                                  13.6ms
[ 78.12%] ··· Running index_object.SetOperations.time_int64_intersection                                6.33ms
[ 81.25%] ··· Running index_object.SetOperations.time_int64_symmetric_difference                        20.0ms
[ 84.38%] ··· Running index_object.SetOperations.time_int64_union                                       12.1ms
[ 87.50%] ··· Running index_object.SetOperations.time_str_difference                                    6.12ms
[ 90.62%] ··· Running index_object.SetOperations.time_str_symmetric_difference                          11.8ms
[ 93.75%] ··· Running index_object.Sortlevel.time_sortlevel_int64                                        775ms
[ 96.88%] ··· Running index_object.Sortlevel.time_sortlevel_one                                         18.2ms
[100.00%] ··· Running index_object.Sortlevel.time_sortlevel_zero                                        20.5ms
```