Merge pull request rust-lang#57 from Noratrieb/bump-2.1.1

Add changelog for 2.1.1

Merge pull request rust-lang#54 from Noratrieb/bump-2.1.0

Bump to version 2.1.0

Merge pull request rust-lang#44 from Nilstrieb/release13

Bump version to 2.0.0 and add changelog

Merge pull request rust-lang#40 from nnethercote/v1.2.0

Bump to version 1.2.0