Official typescript typings

[Strate]

It would be nice to provide official typescript typings.
That typings could be used also for generating documentation, as it done in https://facebook.github.io/immutable-js/

If you accept PRs, I can work on it.

[JerrySievert]

i do accept PRs.

[ruchevits]

🤥

[JerrySievert]

?