Georss-client

* Provide backwards compatibility with v0.15 by exposing constants.

* Removed Python 3.7 support.
* Added Python 3.11 support.
* Added Python 3.12 support.
* Bumped requests to 2.31.0.
* Bumped dateparser to 1.2.0.
* Bumped haversine to 2.8.1.
* Bumped xmltodict to 0.13.0.
* Bumped library versions: black, flake8, isort.
* Migrated to pytest.
* Code quality improvements.

* No functional changes.
* Migrated to github actions.
* Added Python 3.10 support.
* Removed Python 3.6 support.
* Bumped library versions: black, flake8, isort.

* Add license tag (thanks fabaff).
* General code improvements.

* Python 3.9 support.

* Add non-standard namespace used by [EMSC feed](https://www.emsc-csem.org/service/rss/rss.php).