some minor cleaning as well

Supporting python 3.8 as well
adding missing field maps for tests
version checker added
version checker needs all deps installed

updated style
fix in lib_tw, was catching the wrong type of error
adding some tests for lib_tw

correcting the amount of data per step in v11 Density_PAR?

Thanks to Ibon for finding this

and over to documentation pages.

we do not support python 2 anymore

fieldmap already documented this way

bumped version to 2.5.0

use git tag to set version

which we anyway don't use

- we stop supporting python 3.5