fix minor issue in DTL_CEL class

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

we do not support python 2 anymore

bumped version to 2.5.0

a lot of blank except: were replaced,
maybe some of them incorrectly

ess.lib_tw is broken due to removing star imports