Xraydb

Bugfixes:

* change setting the version numbers in the Python code: avoid using `setuptools_scm` in a subfolder of the main git repo. The version number is now hardwired into `setup.cfg` and `xraydb/version.py`, and must be consistent.

- fix several problems with importing database with `sqlalchemy`, now requiring version 2.0.1
- use `platformdirs` to get the configuration folder for the ``materials.dat`` file.
- several doc improvements

* add table of Compton-scattered energies: mean (90 deg scattering) X-ray energies and mean energy of the scattered electron, integrated over angle dependence (Klein-Nishina disrribution)
* use these tabulated mean energies of the Compton-scattered electron in the calculation of ion chamber fluxes.
* add elements up to Z=118 in element table, and add element name (English). No current X-ray data goes that high....
* many small improvements in doc and use of pyproject/setup.cfg
* replace support for Python 3.7 with support for Python 3.11

New features/fixes:

* Add working categories argument to `get_materials()` (Christian Schlepuetz)
* Add functions to calculate sample quantities to get ~1 absorption length for transmission mode XAFS measurements (easyXAFS)
* fix roughness calculation for mirror reflectivity
* allow 'D' and numbers starting with a decimal ('.7') in chemical formulas
* using Github Actions for CI testing