DOC: Clarify what Categorical takes.
REF: Deprecate Factor for Categorical.
ENH/DOC: Allow levels=None for Categorical
TST: Test Categorical constructor with levels=None
DOC: Coherent english in docstring
TST: Test describe method of Categorical
ENH: Add a describe method to Categorical.
REF: Remove Factor alias left by mistake.
ENH: Add levels=None in deprecated class too.
DOC: Factor -> Categorical.
REF: Factor -> Categorical.
BUG: Fix incorrect dtype on groupby with ``as_index=False`` (GH3610_)
Merge pull request #3613 from jreback/groupby_dtype

BUG: Fix incorrect dtype on groupby with ``as_index=False`` (GH3610_)
BUG: Add reduce_if_possible keyword to ``groupby`` to allow reduction from

    DataFrame -> Series if groups are unique. Regression from 0.10.1,
    partial revert on (GH2893_) with (GH3596_)

CLN: renamed reduce_if_possible -> squeeze

DOC: added v0.11.1 example
Merge pull request #3599 from jreback/groupby_output

BUG: Add squeeze keyword to groupby to allow reduction in returned type
ENH add date to DatetimeIndex
document read_csv's usecols argument.
Merge pull request #3544 from lexual/read_csv_doc_usecols

document read_csv's usecols argument.
BUG: (GH3611) Fix read_csv to correctly encode identical na_values, e.g. na_values=[-999.0,-999] was failing
Merge pull request #3615 from jreback/read_csv_na_values

BUG: (GH3611) Fix read_csv to correctly encode identical na_values