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
BUG: Bug in DataFrame construction with recarray and non-ns datetime dtype (GH6140)
Merge pull request #6142 from jreback/from_records

BUG: Bug in DataFrame construction with recarray and non-ns datetime dtype (GH6140)
ENH: Add unique and nunique to GroupBy whitelist

Series.unique and Series.nunique are useful methods for querying the
unique elements (or number of unique elements) in each group when used
in conjunction with DataFrame.GroupBy.  This commit addresses
pydata/pandas#6146.
ENH: Updated tests for series GroupBy whitelist

Added tests for fix to pydata/pandas#6146.
Merge pull request #6147 from bburan-galenea/bburan/groupby-series-unique

ENH: Add unique and nunique to GroupBy whitelist
CLN: fix ScatterCI links in README and rnotes
CLN: convert test docstring to comment
BLD/TST: catch more spurious errors in @network decorator
Merge pull request #6151 from y-p/PR_network

BLD/TST: catch more spurious errors in @network decorator
BLD/TST: one more skip_errno for @network
BUG: fix loc setitem with a dataframe on rhs, multiple items, and a datetimelike (GH 6152)
Merge pull request #6152 from jreback/loc

BUG: fix loc setitem with a dataframe on rhs, multiple items, and a datetimelike
BLD/TEST: @network, SkipTest on known errnos
PERF: perf regression index construction from seris (GH6150)
Merge pull request #6153 from jreback/index_perf

PERF: perf regression index construction from series (GH6150)
TST: rec arrays don't support datetimes in creation on certain platforms, related (GH6140)
TST: dtype comparison issue on windows for (GH6152)