BUG: MultiIndex.get_level_values() replaces NA by another value (#5074)
Make _na_value a class attribute.
Merge pull request #5090 from goyodiaz/multiindex-nan

BUG: MultiIndex.get_level_values() replaces NA by another value (#5074)
DOC: revised io.rst
Merge branch 'timestamp-object-bounds' of https://github.com/danbirken/pandas into danbirken-timestamp-object-bounds

Conflicts:
	doc/source/release.rst
DOC: timeseries.rst updates
TST: use default utf8 encoding when passing encoding to parser as Bytes (GH5141)
Merge pull request #5149 from jreback/sparc_fix3

TST: use default utf8 encoding when passing encoding to parser as Bytes (GH5141)
TST/CI/BUG: fix borked call to read_html testing code
Merge pull request #5151 from cpcloud/read-html-lxml-skips

TST/CI/BUG: fix borked call to read_html testing code
DOC: 5143 (read_html testing bug) release notes
DOC: minor doc correction (issue number) from the previous commit
Merge pull request #5086 from westurner/patch-2

DOC: CONTRIBUTING.md: Gold plating: syntax, punctuation, Markdown format...
BUG: convert replacement tuples to lists

This fixes a bug that makes it appear as if replace is incorrectly using
regular expressions.
Merge pull request #5145 from cpcloud/replace-exact-fix

BUG: allow tuples in recursive call to replace
BUG: Fix to_datetime() uncaught error with unparseable inputs #4928
API/CLN: provide isnull/notnull on NDFrame objects
PERF: remove auto-boxing on isnull/notnull
Merge pull request #5154 from jreback/perf

PERF: remove auto-boxing on isnull/notnull
Merge pull request #5157 from danbirken/gh4928

BUG: Fix to_datetime() uncaught error with unparseable inputs #4928
DOC: Added filtering example to groupby doc

Filtering example for dataframe with > 2 fields -- filtering collapses
to dataframe, not series.