Generate typescript declarations

[Timmmm]

It would be nice if this generated typescript type declarations corresponding to the generated Javascript code.

Or even better, just have a --typescript mode that generates Typescript in the first place.

[mourner]

Yep! Can you give #107 a try?

[rubick24]

https://github.com/rubick24/pbf-compile-ts
I tinkered compile.js a little bit to make it support typescript in my case, but I think it would be better to use Babel to generate ASTs and then output formatted code.