=refactored to have PSF_model and imgen (image generator) as parameters to BDGal.
=comments
=style changes
=made PSF circularizability an option instead of a requirement
=added galsim atmospheric PSF model
=
=can now use voigt and galsim to generate LSST panel1 (similar to voigt+12 figure 4, but using LSST atmospheric PSF
Merge branch 'image_engine'

Conflicts:
	chroma/__init__.py
	chroma/atmdisp.py

Conflicts were minor, just module import stuff.