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

validated on https://icalendar.org/validator.html

bump version to 2.3

(that does not work particularly well)

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