Bump version 0.13.3

Version bump 0.13.2

Merge pull request mkdocs#565 from d0ugal/master

Configuration values can also be str on Python 2.

Version bump to 0.13.0

version 0.12.2

version 0.12.1

version 0.12.0

version 0.11.1

version 0.11

version 0.10