Migrate to typescript

[ericdiviney]

This is not a terribly complex one, just a big one that will have a lot of file changes and due diligence. Eric should probably take this one on.

[M1ck0]

@ericdiviney What do you think about JSDOC instead of TypeScript? It should ensure type safety, but we won't need to change everything. I can take this on if we agree on this approach.