Add typing annotations

[peacememories]

Hi and thanks for maintaining this convenient library. It really makes our management commands look a lot cleaner. What's missing for us at the moment, though, is typing annotations, since we're running mypy on all of our code.

Right now we're working around this by creating a stub for mypy to use, but it would obviously be much better to have first party type annotations. Is this something that's planned/you're interested in adding?

Thanks for considering :)

[FlipperPA]

Good morning! This certainly looks like a worthwhile feature, as long as mypy doesn't become a requirement. Are you interested in working on a PR? Thank you!

[peacememories]

I don't think mypy would need to become a requirement. It would obviously be beneficial to run it on the repo to check our annotations are consistent, but even that is not absolutely necessary. I'm currently a bit busy with a task at work, but once I have free time I would be interested in contributing.