Version 0.12.2.0

Bump version for 0.12.0.0

v0.11.1.0, using React v0.11.1

I'm skipping React v0.11.0 since it included several bugs. We didn't
ship react-rails right away, so it should be find to skip.

Prepare to publish 0.10

Bump version in readme

Update to 0.8.0.0

Update to react-source 0.5.2

Add Appraisal gemfile for therubyracer test