Initial version of TypeScript typings for react-style

This serves partly as documentation and also for integration with either https://github.com/wizzard0/react-typescript-definitions or https://github.com/fdecampredon/react-typescript

Given that Facebook's recently announced Flow type checker for JS uses an annotation format that is syntax-compatible with TypeScript, I'm hopeful that they will eventually provide type definitions for React themselves.

I have some uncertainties around the definitions here:
* Is the Style interface intended to be opaque or should the className and isCompiled attributes be public?
* Is ReactStyle.create() meant to be public or is that just an implementation detail?
This should be `compile(): {classNames: Map<string, bool>, css: string}`