Rename, reorganize and update CHANGELOG for missing releases.

Followed a format I've described at http://keepachangelog.com:
- Added release changes for 1.1.0, 1.1.1, 1.1.2, 1.1.3, 1.1.4, 1.1.5
1.1.6, 1.1.7, and 2.0.0.
- Added headings ("Fixed", "Removed", etc.)
- Added proper punctuation.
- Modified unordered list syntax (use - instead of *).

Let me know if this is okay. :smiley: