model API changes.
model API changes.

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