API: add 'level' kwarg to 'Index.isin' method

PERF: optimize MultiIndex.isin when level != None

DOC: update doc bits on Index.isin and MultiIndex.isin

DOC: merge isin sections for container & index classes

DOC: make isin a separate section

It's no longer a subsection of boolean indexing.
BUG/DOC: Categoricals now raise NotImplementedError when writing to HDFStore with a Fixed type store (GH7918)
         Slicing bug with a single-dtyped category and a possible view
Merge pull request #7892 from immerrr/add-level-kwarg-for-index-isin

API: add 'level' kwarg to 'Index.isin' method
Merge pull request #7924 from jreback/cat_fixes

BUG/DOC: Categorical fixes (GH7918)
BUG: Bug in to_datetime when format='%Y%m%d and coerce=True are specified, where previously an object array was returned (rather than
     a coerced time-series with NaT), (GH7930)
Merge pull request #7931 from jreback/dt_format

BUG: Bug in to_datetime when format='%Y%m%d and coerce=True are specified (GH7930)
update to holiday to help with GH#7070