TST7337: Disallow use of dateutil tzfile objects whose filename contains '.tar.gz'.
TST7337: Fix test failures on windows.

Avoid constructing dateutil timezones explicitly because of filename issue.
Use dateutil.tz.tzutc() to construct UTC timezone instead of
dateutil.tz.gettz('UTC')
Update docs to reflect this.
Tidy up examples in the timezones section of the docs.
Add test for conversion between dateutil.tz.tzutc() and dateutil.tz.gettz('UTC')
BUG/OUTPUT: fix repring of MI nat

Fix neg indexers in datetimeindex
make nanops._maybe_null_out work with complex numbers ( issue #7353 )
support axis=None for nanmedian ( issue #7352 )
make nanops work when ndim==1 and axis==0 ( issue #7354 )
Make nanops._has_infs work for additional dtypes and multidimensional arrays ( issue #7357 )
remove warning about coercing complex values
add tests for nanops
move nanops._ensure_numeric tests to test_nanops.py
minor nanops pep8 fixes