BUG: DataFrame.stack(..., dropna=False) with partial MultiIndex.
COMPAT: windows compat for tests for dtype inference in parser xref (GH8833)
BUG/ENH: cleanup for Timedelta arithmetic

Fixes GH8813
Fixes GH5963
Fixes GH5436

If the other argument has a dtype attribute, I assume that it is ndarray-like
and convert the `Timedelta` into a `np.timedelta64` object. Alternatively, we
could just return `NotImplemented` and let the other type handle it, but this
has the bonus of making `Timedelta` compatible with ndarrays.

I also added a `Timedelta.to_timedelta64()` method to the public API. I
couldn't find a listing for `Timedelta` in the API docs -- we should probably
add that, right?

Next up would be a similar treatment for `Timestamp`.
Merge pull request #8896 from pydata/winfix4

COMPAT: windows compat for tests for dtype inference in parser xref (GH8833)
Merge pull request #8884 from shoyer/fix-timedelta-math

BUG/ENH: cleanup for Timedelta arithmetic
DOC: v0.15.2.txt fixups
BUG CSV: fix problem with trailing whitespace in skipped rows, issues 8661, 8679
ENH CSV: Reduce memory usage when skiprows is an integer in read_csv, issue 8681
Merge pull request #8752 from selasley/trailing_spaces_fix

Update tokenizer to fix #8679 #8661
BUG: DatetimeIndex with time as key
Fix unrecognized 'Z' UTC designator
Merge pull request #8832 from broessli/z-utc

Fix unrecognized 'Z' UTC designator
Doc change for Issue #8805
Merge pull request #8912 from vvbchaves/master

DOC: Issue #8805
DOC: specify return type in to_datetime
CLN: move import to top of file

For consistency with [PEP8][1]:

    Imports are always put at the top of the file, just after any module
    comments and docstrings, and before module globals and constants.

[1]: https://www.python.org/dev/peps/pep-0008#id17
Merge pull request #8922 from aevri/refactor/move_import

CLN: move import to top of file
BUG: Option context applies on __enter__

Option context no longer overrides options when used outside a `with`
statement.

Added test TestConfig.test_option_config_scope

Closes #8514
Merge pull request #8921 from jorisvandenbossche/docstring-to_datetime

DOC: specify return type in to_datetime
BUG: moving the utf encoding line to the first line (before from __future ..)
Merge pull request #8925 from hkleynhans/fix/8514_option_context_with

BUG: Option context applies on __enter__