trying python 3.7 instead

fixed incorrectly detected error by mypy on some systems
black has reformatted code after update

added support for strings
this is a bit more tricky so issues could arise

also fixed ess.__name__
see https://packaging.python.org/guides/single-sourcing-package-version/

(which I think is currently 3.9 that does not fully work)

added more options to the data file

this is the first list of options added

includes support for converting 3D quad fields
found a minor error in field_on_axis, slightly wrong mid index was selected
some minor cleaning included