Add py.typed and typing

[Goldziher]

Hi,

This library is untyped:

nlp/sentiment.py:1: error: Skipping analyzing "textblob": module is installed, but missing library stubs or py.typed marker  [import-untyped]
nlp/sentiment.py:8: error: Type of variable becomes "Any" due to an unfollowed import  [no-any-unimported]
nlp/sentiment.py:9: error: Type of variable becomes "list[Any]" due to an unfollowed import  [no-any-unimported]

To fix this, a py.typed file has to be included in the package. Additionally, it should actually be properly typed.

[johnfraney]

@sloria This is something I can chip away at if you'd like to assign it to me!

[sloria]

@johnfraney go for it!