Typescript support

[jadbox]

Thanks for writing this! It would be awesome to get TS support.

[Andarist]

Hi! I've started working on this - but getting this right ain't the simplest thing in the world. Gonna continue working on the generic version, if I fail in the end I'm gonna provide inded.d.ts with overloads.

EDIT: generic version of those typings is currently blocked by microsoft/TypeScript#29919