Add TypeScript typings

[pschyma]

This PR adds typings to allow for an easier integration in TypeScript based projects.

All types are extracted from the source files and the documentation. Here the values found in the source code take precedence. For example the type of the changeRating handler is ((rating, name?) => void) | null with a default of null instead of () => {} like stated in the documentation.

This also fixes #10 in TypeScript projects, because I added the corresponding property to the component, since the feature is already implemented but the propTypes lack the correspondig property whilst its default is set to Star.

[ergofriend]

Pls create a new npm package for typescript :)

[blimpmason]

When will this be merged?

[mayinghan]

can this pr get merged?