DOC: moved numpydoc sphinx extension to subdirectory

Clearer distinction from ipython directive files
DOC: update numpydoc to current master (commit 223df02530)
CLN: ipython expects None from _repr_html_ to signal no html repr GH5922
Merge pull request #6045 from y-p/PR_ipython_repr_html

CLN: ipython expects None from _repr_html_ to signal no html repr GH5922
DOC: minor doc edits
Add -NaN and -nan to default NA values
Merge pull request #6038 from Bklyn/master

Make -NaN and -nan default NA values
BUG: Regression in .get(None) from 0.12 (GH5652)
Merge pull request #6053 from jreback/get

BUG: Regression in .get(None) from 0.12 (GH5652)
TST/DOC: addtl tests and docs for (GH6056)
Merge pull request #6058 from jreback/iloc_segfault

TST/DOC: addtl tests and docs for (GH6056)
BLD: add IPython and sphinx to show_versions #6059
Merge pull request #6064 from y-p/PR_add_deps_show_versions

BLD: add IPython and sphinx to show_versions #6059
Merge pull request #6003 from jorisvandenbossche/numpydoc

DOC: update numpydoc to current master (commit 223df02530)
API: Add equals method to NDFrames. (Implemented with `array_equivalent`, which is similar to `np.array_equal` except that it handles object arrays and treats NaNs in corresponding locations as equal.

TST: Add tests for NDFrame.equals and BlockManager.equals

DOC: Mention the equals method in basics, release and v.0.13.1