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

added files: fieldmapy.py: has several functions which are useful for manipulating the data for TraceWin fieldmaps
                   SP_Relativity: has several function which return relativistic beta and gamma from energy and vice versa
		    TTF.py: has few functions for calculating TTF of cavity fieldmaps
added example: Scan_Energy_gain_in_fieldmap-v16.pynb which has several functions and examples for phase scan (to be completed)

added command line arguments

(unsure how this worked before)

new function plt.get_dst returns a dst object
function plt.save_dst forces you to provide a file name (and use get_dst)

- current convert A vs mA
- forgot to write mass (= mc2)
- using file write() rather than print function
print was not working correctly on both python2 and 3
this has been tested to give correct result on both

(was not working on my python2)
added plt.save_dst()
fixed pack function in dst.save() for python3

replaced xrange -> range (py3 compatibility)

made sure forward compatibility is preserved

made all print statements python3 safe
absolute import