Bump version to 4.1.1

Most important changes are fixing `log>=0.4.15`.

Adding the new feature (support for `log/unstable_kv`) could
arguably require bumping the minor version (-> 4.2.0)

However, since it's an unstable feature so I don't consider
that necessary.

Bump version

Merge pull request #11 from eranrund/master

update changelog, bump version.

version 3.0.1

version 2.0.0-3.0

version 2.0.0-1.0

version 2.0.0-0.1

version 0.2.0