💫 Tidy up and auto-format .py files

[ines]

Description

• Use black to auto-format all .py files.
• Update flake8 config to exclude very large files (lemmatization tables etc.)
• Update code to be compatible with flake8 rules
• Fix various small bugs, inconsistencies and messy stuff in the language data
• Update docs to explain new code style (black, flake8, when to use # fmt: off and # fmt: on and what # noqa means)

Once #2932 is merged, which auto-formats and tidies up the CLI, we'll be able to run flake8 spacy actually get meaningful results.

At the moment, the code style and linting isn't applied automatically, but I'm hoping that the new GitHub Actions will let us auto-format pull requests and post comments with relevant linting information.

Types of change

enhancement, code style

Checklist

• I have submitted the spaCy Contributor Agreement.
• I ran the tests, and all new and existing tests passed.
• My changes don't require a change to the documentation, or if they do, I've added all required information.