The goal here is to provide perfect TypeScript types for customers using the module. Generally when doing this work I like to:

1. enable noImplicitAny in the tsconfig
2. Choose a single file to get passing, and fix all errors in that file (using VSCode here is really useful)
3. disablenoImplicitAny
4. Get all the tests passing
5. Submit a PR for just the single file I updated
6. Repeat until finished

It's a lot easier if we do a PR per file on this one.