ENH: Import testing into main namespace.
TST: run clipboard tests explicitly
DOC: clarify docstring of rolling/expanding moments

- document center argument
- add note about the result set at right edge by default
- clarified freq keyword a little bit
DOC: fix doc build warnings
CLN: Specialize assert_(np.array_equal(...))

Work on #6175. This is the second half of the work started in #6368.
BUG: DataFrame.shift with axis=1 was raising (GH6371)
Merge pull request #6373 from jreback/df_shift

BUG: DataFrame.shift with axis=1 was raising (GH6371)
Merge branch 'explicit-cb' of https://github.com/cpcloud/pandas into cpcloud-explicit-cb

Conflicts:
	doc/source/release.rst
PERF: fix series slice indexing performance
API/BUG: reindex_like not passing copy/limit kwargs thru
Merge pull request #6372 from immerrr/fix-perf-for-series-slices

PERF: fix performance for series slices (even more)
Merge pull request #6374 from bwignall/assert_6175_arrayequal_2

CLN: Specialize assert_(np.array_equal(...))
PERF: take the fast path on a reindex when reindexers are identical
BUG: fix nested dict bug
DOC: release notes
checkin of percentage rank
Merge pull request #6365 from cpcloud/replace-nested-dict-6342

BUG: fix nested dict replace
Merge pull request #5978 from MichaelWS/master

ENH: series rank has a percentage rank option
TST: more catching of network errors
BUG: Bug in take with duplicate columns not consolidated (GH6240)