FIX: 'parser_trim_buffers' properly initializes word pointers
### Summary

The pull request:
- [x] closes #13703;
- [x] passes all tests in `test.sh` except one (see the output);
- [x] passes the code style test `git diff upstream/master | flake8 --diff`;
### Details

Basically the function [**parse_trim_buffers**](https://github.com/pydata/pandas/blob/master/pandas/src/parser/tokenizer.c#L1217) did not properly move word pointers in **parser->words** and related fields. This pull request aims at fixing that.

Changes in **parse_trim_buffers**:
- block **L1239 -- L1256** (**/&ast; trim stream &ast;/**) was augmented with **parser->words** update loop;
- blocks **L1224 -- L1237** (**/&ast; trim words, word_starts &ast;/**) and **L1239 -- L1256**(**/&ast; trim stream &ast;/**) were swapped to preserve pointer consistency;
### Output of `test.sh`:

```
======================================================================
FAIL: test_round_trip_frame_sep (pandas.io.tests.test_clipboard.TestClipboard)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/ivannz/Github/pd_fork/pandas/pandas/io/tests/test_clipboard.py", line 73, in test_round_trip_frame_sep
    self.check_round_trip_frame(dt, sep=',')
  File "/Users/ivannz/Github/pd_fork/pandas/pandas/io/tests/test_clipboard.py", line 69, in check_round_trip_frame
    tm.assert_frame_equal(data, result, check_dtype=False)
  File "/Users/ivannz/Github/pd_fork/pandas/pandas/util/testing.py", line 1276, in assert_frame_equal
    right.columns))
  File "/Users/ivannz/Github/pd_fork/pandas/pandas/util/testing.py", line 1022, in raise_assert_detail
    raise AssertionError(msg)
AssertionError: DataFrame are different

DataFrame shape (number of columns) are different
[left]:  2, Index([u'en', u'es'], dtype='object')
[right]: 0, Index([], dtype='object')

----------------------------------------------------------------------
Ran 10377 tests in 1197.728s

FAILED (SKIP=363, failures=1)
```

Apart from this, there were a couple of _deprecation warnings_ in files other that _tokenizer.c_.
