Aiosql

- add `duckdb` support
- switch to `pyproject.toml` only configuration
- rename `master` to `main`
- improve some docs
- remove python 3.7 support and simplify code accordingly

- make select an iterable
- support `/* ... */` comments
- warn on strange query names

Fix overlapping re issue with `:v+:w` which was missing detecting the second variable.

Improve testing.

Features:
- add MariaDB support
- allow to change file extension when loading directories
- switch `mysql.connector` dependency to `mysql-connector-python` because `mysql-connector` is obsolete
- improved documentation

Tests:
- simplify github CI tests, no service needed
- run from Python 3.7 to 3.11
- extensive rework of tests to ignore missing modules, use marks…
- add tests with docker images, needed for mariadb
- depend on pytest 7.

- improved documentation
- add missing dependency on `setuptools`
- improved Makefile
- add untested `mariadb` support (will be tested and advertised in the next release)
- some refactoring (for next release really)