Add typescript definitions

[maddijoyce]

What: Adding typescript definitions

Why: The types for some parts of the dom-testing-library are currently in use in react-testing-library. Really these should be stored alongside the appropriate code and then imported as needed.

How: Added d.ts files with definitions to match functions. Some definitions pulled from react-testing-library (thanks @alexkrolick and @InExtremaRes).

Checklist:

• Documentation N/A
• Tests
• Ready to be merged
• Added myself to contributors table

I think adding dtslint is a good first step as far as keeping the definition files tested and avoiding types issues (as per testing-library/react-testing-library#82).

The types are only compatible with TypeScript 2.8 and up, because I've used mapped types for the bindElementToQueries function. It's possible to avoid using mapped types, but it means duplication of a lot of the queries code, and I think it's better to avoid that.

If you're happy with these types, I can update the react-testing-library to use them once everything has been merged.

[maddijoyce]

Also fixed a small error in events.js.
The copy event was using a CompositionEvent not a ClipboardEvent

[kentcdodds]

Looks great to me! I'm going to call this good considering your our TypeScript maintainer 😉

[kentcdodds]

Thanks so much for your help! I've added you as a collaborator on the project. Please make sure that you review the other/MAINTAINING.md and CONTRIBUTING.md files (specifically the bit about the commit messages and the git hooks) and familiarize yourself with the code of conduct (we're using the contributor covenant). You might also want to watch the repo to be notified when someone files an issue/PR. Please continue to make PRs as you feel the need (you can make your branches directly on the repo rather than your fork if you want). Thanks! And welcome to the team :)