Typescript typings support
I am currently writing typings for react-sketchapp. I plan on publishing these typings to `@types/react-sketchapp` but an alternative to that is having the typings included in this repo itself. [This is done by including a `typings` field in the `package.json` that references a typings file (e.g. `react-sketchapp.d.ts`)](https://www.typescriptlang.org/docs/handbook/declaration-files/publishing.html#including-declarations-in-your-npm-package).

Including the typings first-party enables better typescript support as well as better javascript support (without a typescript dependency) for editors that use the typescript language service.

Proposal:

If you give me your blessing, I'd like to fully type this library and include those typings in a pull, else it's going to `@types/react-sketchapp`.