Aiopywttr

- Add support for Galician language.

- Allow keyword-only arguments of public methods to be positional.

- Raise minimum required Python version from 3.7 to 3.7.2.
- Add docstring to `__init__.py`.
- Add `from __future__ import annotations` to all modules.
- Use relative imports.

- Remove unsupported languages.

- Update dependencies.

- Use `__slots__`.