BUG: Fix to_datetime to properly deal with tz offsets #3944

Currently for certain formats of datetime strings, the tz offset will
just be ignored.
DOC: Clarify that DataFrame string formatters must return strings

I am not 100% sure that string formatters must really return *unicode* strings
(non-unicode strings seem to work, too), but I am leaving that because it's
what is already documentated.

Fixes #6052.
ENH: allow legend='reverse' in df.plot() GH6014
CLN: clear up some cython warnings
CLN: eliminate bootstrapping issue form generate_code.py
ENH: Import testing into main namespace.
CLN: test_timeseries_legacy, specialize assert_

GH6175: replacing "assert_" with specialized form assertEqual. WIP: have not adjusted any instances of assert_( (... == ...).all() )
CLN: test_timeseries, specialize assert_

GH6175: replacing "assert_" with specialized form assertEqual. WIP: have not adjusted any instances of assert_( (... == ...).all() )
DOC: add links to other pages to contributing.rst
Fix typo in Melt section
BUG: dont ignore use_index kw in bar plot
Merge pull request #6211 from Bklyn/doc-fix

DOC: Fix typo in Melt section
BLD: more exception message skipping in @network
BLD/DOC: make.py open file as 'w' rather then 'wb'
BLD/DOC: ip_directive use py3 compat text_type
CLN: typo
Merge pull request #6210 from TomAugspurger/bar-use_index

BUG: dont ignore use_index kw in bar plot
BLD: Cut Travis-CI build times by 30-50%
foo
Merge pull request #6218 from y-p/ironcache

BLD: Cut Travis-CI build times by 30-50%