[FR] Type hint the source code

**Is your feature request related to a problem? Please describe.**
When developing with this library, I constantly have to type hint variables returned by the functions, so my autocompleter suggests the right properties and for cleaner code.

**Describe the solution you'd like**
It would be great if you could type hint the library or at least the public API in order to help type checkers, autocompleters and collaboration.

**Describe alternatives you've considered**
None

**Additional context**
None