Add alpha.py and phase_shifts.py

Required for plotting phase shift as a function of phase angle
for an asteroid.
make arguments optional: asks them if not given
Integrate deltaphi.py
better commenting, remove created temp files
change print to abs value
add deltaphi
rename alpha.py to gen_phasetable.py
delete alpha
add descriptive comment at start
Merge branch 'master', remote-tracking branch 'origin/master'