BUG: Fix segfault on isnull(MultiIndex)

Now raises NotImplementedError b/c not yet clear what it should return.
Merge pull request #5125 from jtratner/fix-segfault-mi-isnull

BUG: Fix segfault on isnull(MultiIndex)
TST: addtl pytables tests
Merge pull request #5180 from jreback/pytables_clean

TST: addtl pytables tests
DOC: multi-index update on cookbook.rst
DOC/CLN: fix a few typos that were causing Sphinx warnings
DOC/CLN: Fix a plural NaN type since Sphinx cannot parse that
DOC/CLN: clean up the interpolate docstring a bit
DOC/CLN: remove numpydoc-invalid keyword arguments section
DOC/CLN: elaborate on infer_types/parse_dates interaction
DOC/CLN: wrap bq examples so that they do not require scrolling