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

Update SP_Relativity.py with functions emit_geo and emit_norm which return the geometrical and normalized emittances

bump version to 2.3

and a little import cleaning

renamed fieldmapy -> fieldmap
split out example for fieldmap, added map files for testing
some minor  modifications of the functions

using meshgrid for the data
added interpolation function

moving examples out of sources