add ah_bootstrap.py script from v0.4.3 astropy-helpers
add ah_bootstrap.py script from v0.4.3 astropy-helpers

kbarbary/sncosmo,kbarbary/sncosmo,sncosmo/sncosmo,dannygoldstein/sncosmo,sncosmo/sncosmo,dannygoldstein/sncosmo,kbarbary/sncosmo,dannygoldstein/sncosmo,sncosmo/sncosmo