BUG: Fix DatetimeIndex.insert() with non-datetimes.

Coerces to object Index instead.
COMPAT: allow string concats to datetimeindex only (int/float are invalid)
DOC: moved numpydoc sphinx extension to subdirectory

Clearer distinction from ipython directive files
DOC: update numpydoc to current master (commit 223df02530)
TST: fix test that repr returns str
BUG: less false positives with SettingWithCopy (GH6025)
Merge pull request #6040 from dsm054/fix-test-that-repr-returns-str

TST: fix test that repr returns str
BUG: Bug in setting using fancy indexing a single element with a non-scalar (e.g. a list),
    (GH6043)
Merge pull request #6044 from jreback/ix_list

BUG: Bug in setting using fancy indexing a single element with a non-scalar (e.g. a list) (GH6043)
Merge pull request #6042 from jreback/setting_with_copy

BUG: less false positives with SettingWithCopy (GH6025)
DOC: add guidelines for building the docs
DOC: add section contributing to pandas

+ link to README.rst in /docs
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)
PERF: Speed up pd.to_datetime() by optionally inferring dt format #5490

Given an array of strings that represent datetimes, infer_format=True
will attempt to guess the format of the datetimes, and if it can infer
the format, it will use a faster function to convert/import the
datetimes.  In cases where this speed-up can be used, the function
should be about 10x faster.