Add 2.1.1 changelog item.
More ChangeLog files edits.

Made tab/space usage in reST consistent back to 2.1.0 entry. Also update
ChangeLog_highlights.rst for 2.1.1.
Thank our contributors. [skip-ci]
Remove release date for now.
Merge pull request #284 from pymssql/changelog-2.1.1

Changelog file section for 2.1.1 release [WIP]