Add `mypy` hook to pre-commit

[slsh1o]

I'm not sure what else should I add to mypy.ini. Something related to tests or maybe to sphinx.

And also there are some errors which idk how to fix better.

Ref: #16

[slsh1o]

Slightly reorder mypy.ini but I'm still not sure how to cure raised errors.

[webknjaz]

but I'm still not sure how to cure raised errors

First, try exploring what causes these errors. Then, we'll decide how to deal with each of them.

[webknjaz]

src/sphinxcontrib/towncrier/_version.py:5: error: Cannot find implementation or library stub for module named 'towncrier._scm_version'
src/sphinxcontrib/towncrier/_version.py:5: note: See https://mypy.readthedocs.io/en/latest/running_mypy.html#missing-imports

Try creating a stub file for _scm_version: https://mypy.readthedocs.io/en/stable/stubs.html.

[webknjaz]

src/sphinxcontrib/towncrier/__init__.py:55: error: Incompatible types in assignment (expression has type "Tuple[str, str, str, str]", variable has type "Tuple[str, str]")

I guess mypy "sees" the initial declaration that is Tuple[str, str] and automatically decides that it's the final type. You should probably mark it as something like iterable explicitly.

[webknjaz]

src/sphinxcontrib/towncrier/__init__.py:80: error: "Dict[str, Any]" has no attribute "release"
src/sphinxcontrib/towncrier/__init__.py:82: error: "Dict[str, Any]" has no attribute "version"

This is just an incorrect annotation. It's best to figure out what type it is really. Maybe stick a debugger there...