Gravitational lens class now can plot both deflection angles side-by-side.  Also have created file for source images. Fixes #13
Added source file.  Doesn't do much yet, although it can read from an image.
Added lensed image test ipython notebook, with documentation.  Fixes #24
added source object with options to load a fits image (it builds grid similar to kappa map, except its angles are beta instead of theta).  Fixes #22
Gravitational lens object now has option to raytrace itself.  Fixes #23.  Plotting options for pre and post lensing are also available.  Fixes #25
added python script to turn RBG JPG image into black and white FITS image.  WARNING:  Does not write NAXIS1 and NAXIS2 correctly.
updated init file to initialize source.py.  Also changed deflection angle test so that it plots the error in alpha_y (will improve later).
Update README.md

Added link to lensed image test ipython notebook to show off first Einstein rings.
modified add operator to enable composit lenses.  Adds kappa maps and deflection angles for each pixel.  Current restrictions:  Array dimensions and pixel scales of the two lenses must be the same. Works Towards #17
modified sub operator so that differences in kappa,alpha between two maps can be estimated.  Probably other uses also.  Limitation:  Can only be done with kappa maps of same shape and pixscale. Fixes #17
New ipython notebooks have more plots and tests.
making sure this branch is up to date.
fixed unit problem that was giving einstein radius in radians instead of arcsec.
source.py now is more flexible with rectangular images converted to FITS from JPEG.  JPGconverter.py now has pixel sizes that correspond to the images in the lensed image test (can be made more general in the future).
conclude merge.
Added interpolation to raytrace method to improve smoothness.  Fixes #28
source functions and raytracing now incorporates data cubes.  Fixes #29
build_kappa_map function now allows user to specify sigma,centroid,and axis ratio of an SIElens.
raytrace function now has header
all three lenses now have different parameters through customizing build kappa map function