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.
DOC: Added Categorical improvements to release notes
Merge branch 'categorical-cleanup' of https://github.com/jseabold/pandas into jseabold-categorical-cleanup

Conflicts:
	RELEASE.rst
TST: changed test_factor -> test_categorical