substantial cleanups of APIs:
changed pmModelGroup to pmModelClass
dropped the _GetFunctions, and moved the modelClass-specific functions
to functions pointers in the pmModel structure. These are assigned
when the model is allocated, based on the model type. Now, instead of
calling, for example,
modelFunc = pmModelFunc_GetFunctions(model->type)
modelFunc();
you just do:
model->modelFunc()
moved some of the support functions into pmModelUtils and
pmSourceUtils.
changed pmIsFooBar to pmFooBarTest for better api listing.
added functions to evaluate and add/subtract models applying an offset
between the image coordinate frame and the chip frame (required frame
for model parameters)
added function(s) to instatiate a pmModel from a pmPSF based on a
given coordinate and peak flux.
added a function to set the model normalization based on a source flux
value.
