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

Coerces to object Index instead.
COMPAT: allow string concats to datetimeindex only (int/float are invalid)
BLD: erase local ipython_directive
BLD: pull in latest ipython_directive from ipython 0355d3d
BLD: ipython_directive, add back okexcept
BLD: ipython_directive, enforce tight layout for mpl plots
BLD: ipython_directive, cython magic fix
BLD: make io.rst utf8-safe GH5142 GH5926
BLD: ipython_directive, decode ipython output as utf8+replace
BUG: use the "join" string in Appender decorator

The docstring for Appender decorator says that "join" parameter is used to join the docstring and addendum.  This commit brings the code in line with the documentation.
DOC: tutorials
DOC: whitespace fixes for tutorials update GH5929
Change "methdo" to "method" in asfreq's docstring.
Merge pull request #5989 from  adeodatus/master

* adeodatus-master:
  Change "methdo" to "method" in asfreq's docstring.
Merge pull request #5959 from gandalf013/master

BUG: use the "join" string in Appender decorator
BUG: don't lose dtypes when concatenating empty array-likes
Merge pull request #5742 from immerrr/dont-lose-dtype-concatenating-empty-arraylikes

BUG: don't lose dtypes when concatenating empty array-likes
Merge pull request #5925 from y-p/PR_rebase_ipython_directive

Rebase ipython_directive on top of recent ipython updated version
DOC: document read_csv fastpath for iso8601 datetime strings
Merge pull request #5993 from y-p/PR_doc_iso8601_fast_path

DOC: document read_csv fastpath for iso8601 datetime strings