added new plotting features and calculated deflection angles numerically
Update README.md
Added deflection test plan of attack, fixes #8
Merge branch 'master' of github.com:wmorning/EvilLens
added separate grid for alpha.  No operations currently added that use this grid.  Progress toward #15
added comments to setup_grid function to describe the addition of the image/source grid.
code now uses the new image grid to compute deflection angles.  Also doesn't plot contours when plotting the deflection angles (although it could easily be made to do so).  Fixes #15
Cleaned up commented lines that had become useless.  Also successfully tested shifting the centroid position.  Fixes #16
Changed write kappa method so that it includes pixscale in header.  Fixes #18 .  Also changed units in build kappa map so that it follows Saas Fe, and analytic solution so that it has the same consistency.
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.