Adding mixin support

Mixins are really helpful and awesome so I hope to use them more.
Updating documentation for mixins
Removing the react-addons typings

They are no longer required.
Improving the npmignore

We now include the typings
3.0.0
Update README.md
Trying to add auto release

This will improve integration with npm.
Merge branch 'mixins' of github.com:Asana/typed-react into mixins
Merge pull request #34 from Asana/mixins

Adding mixin support