- more consistent module names
- removing a duplicate
- fixing new flake8 warnings

updated style
fix in lib_tw, was catching the wrong type of error
adding some tests for lib_tw

ess.lib_tw is broken due to removing star imports

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)

SP_relativity and TTF added. They contain sets of functions to calculate beta, gamma and energy from each other and calculating the TTF and input phase for max energy gain in a field map.