ENH: Add `isin` method to DataFrame.

docs. to be rebased

ENH: Add isin method to DataFrame

Basic tests.

Added method and fixed tests.

ENH: Add ordered argument to df.isin()

Expects a sequence of arrays.

Updated release notes for df.isin()

CLN: cleanup

going to remove ordered argument.

Using a dict for ordered matching. Docs

BUG: fixed subselection length check issues.

Updated release notes for df.isin()

remove merge conflict note
ENH tweak DataFrame isin method
ENH add iloc argument to DataFrame isin
TST: change a small float comparison to np.allclose
DOC: cookbook addition
Merge pull request #4307 from jreback/ujson_small_fix

TST: change a small float comparison to np.allclose (GH4306)
DOC: add 0.13 to release notes
TST: make sure test passes even if componnents link isn't present
Merge pull request #4310 from cpcloud/network-failure-hack

TST: make sure test passes even if components link isn't present
DOC: cookbook example
RLS: set released to True, edit release dates
RLS: edit windows note about numpy build version
Merge pull request #4258 from hayd/dataframe_isin2

ENH: Dataframe isin2