Convert to typescript

[awinograd]

@samuelgozi , interesting in trying out your library. I noticed you were planning to convert to typescript, so I gave it a first pass here. Let me know what you think

I left some of the types I wasn't sure about as unknown where possible

[samuelgozi]

Thank you very much for your contribution.
I indeed want to migrate to typescript, but I want it to be the last thing before the 1.0 release because the API might change and I don't feel yet as confident as I do with plain JS.

Another thing I wanted to do is to test bundle sizes vs plain JS. I don't expect the change to be significant, but I do want to know the difference.

I'm sorry if I wasn't very clear about that, I just didn't expect a contribution that soon.
I will leave the pull request open up until I decide how to proceed with it.

And again, Thank you!

[awinograd]

Not a problem. Feel free to take it or leave it. If the changes aren't too significant, it's likely not a ton of work to incorporate them into my fork