pep8
add 2.0 release to changelog
Changelog proofreading
Remove non-existant 1.2beta2dev release

There has never been a 1.2beta2dev release. The corresponding entries
are now subsumed under 2.0.
Add / fix / extend some changelog entries
Merge pull request #701 from liqd/feature-update-changelog+

Update changelog for upcoming release 2.0