update project file license and supported Python versions

another fix for generating pdf of doc

back to setting version string by hand

update zenodo link in doc

some more doc tweaks

not using setuptools_scm to auto-set version from git tags: setup.cfg…

… and xraydb/version.py need to agree

update versions of setuptools, add note on wheel building

fix setup

Merge pull request #23 from easyXAFS/master

Transmission sample calculation bug fix; add molar_fraction to output of transmission_sample

drop travis, use github actions