Stubs for static type checker like mypy #112

Hi!

I am using the elmclient in a project and I really like static type checkers like mypy.
So I started to create .pyi stub files for your code and released the in my stubs repo.

Are you interested in moving theses to your code?
I can offer to complete it for (almost) the entire current codebase and you would just need to copy them to ELM-Python-Client.

Of course you would have to continue to maintain it afterwards, but that should be relatively easy after the initial work.
But I think it would help a lot of people out there!

Cheers