Propose docstring style for repo

[smaye81]

Here is a proposal for how to structure docstrings in protovalidate-python going forward (at least when porting the rest of the validation implementations). I think this strikes the right balance of adhering to best practices while not being onerous.

• Functions being added to the library should get the bulk of the comment description in a docstring. No need to define Args:, Raises:, etc. though.
• Any other public function, class, etc. should preferably have docstrings, though not necessary.
• Be as succinct as possible while also keeping comments across implementations consistently worded.

For validation following an RFC / spec:

• Always include any relevant ABNF grammar and keep aligned.
• Indent grammar inside docstring.

One suggestion outside the scope of this PR might be to always have full docstring (Args, Raises, etc.) on any public method the user interacts with (i.e. stuff in validator.py)

[timostamm]

👍

[smaye81]

@timostamm made even more consistent with other implementation comments here: 001449d.

is_uri_reference wouldn't pass a linter, but we can worry about that if we ever turn one on for docstrings.