Merge pull request pypa#139 from pypa/release-24.0

Release 24.0

Merge pull request pypa#131 from di/release-23.0

Release 23.0

Merge pull request pypa#119 from pypa/release-22.0

Release 21.0

Release 20.0 (pypa#93)

Release 19.0 (pypa#86)

Change Github-flavored Markdown identifier to 'GFM'

Release 18.0 (pypa#72)

* Gracefully handle new exceptions from bleach.

Released v17.2

* Fix an issue cleaning plaintext values.