Feature request: Add support for typing with mypy

[lindycoder]

Problem:

Using the aws_encryption_sdk in a project with mypy produces this error:

error: Skipping analyzing "aws_encryption_sdk": module is installed, but missing library stubs or py.typed marker

Solution:

I attempted to simply add the py.typed marker file to my virtualenv and it seems not as simple, a lot of other incompatibilities.
Maybe stubs or .pyi could be provided

Thank you very much!

[texastony]

@lindycoder

Thank you for the Feature Request.
We will try and improve our typing support.

Leaving open as an enhancement.

[harivamsi9]

Hey! Is this issue still open?
Can I take this as my first issue and contribute?