Add TypeScript definitions

[claabs]

I had added types for my own project, and thought I should just spin up a PR so it wouldn't get lost.

The types are based mostly on the docs. Some functions were in the tests, but missing from the docs, so they were added as well. I didn't do too much digging through the C code, so there may be more exposed functions missing from the types. I can at least confirm that all the functions tested are typed.

I added docs to the types based on the docs site when they added value.

[claabs]

There's some typos I've found, so not ready to merge yet.

[rimmartin]

Ah ok, when you are ready