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
CLN: remove try suite in _read

A skip will now occur if a call to urlopen or a read from the resulting object
throws a urllib2.URLError exception
DOC: cookbook example
TST: skip some tests if scikits is installed but not scipy GH3376
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
DOC/CLN move isin to 0.13 release note
DOC: add v0.13.0.txt to the index.rst (closes GH4288)
Merge pull request #4305 from cpcloud/add-urlerror-info

CLN: let URLError fall through in pandas.io.html._read
DOC: correct release notes version
Merge pull request #4349 from cpcloud/add-urlerror-info

DOC: correct release notes version
Merge pull request #4320 from y-p/GH3376

TST: skip some tests if scikits is installed but not scipy GH3376
BLD: Use git describe to generate the version string for dev versions
BLD: Strip leading v in git describe version string
DOC/BUG: fix doc build error because a frame was being redefined
BLD: remove ISRELEASED flag
Merge pull request #4218 from y-p/PR_dev_version_string

BLD: Use 'git describe' to generate the version string for dev versions