fake data for astrometry

I spent a little time working on making fake data for functional testing of the internals of astrometry.net. In particular, we started to get afraid that we aren't completely consistent with the FITS convention that the center of the first pixel in an image array get (x,y) coordinates (1.0,1.0). We have software kicking around that makes the center of this pixel (0.5,0.5) and most of our IDL code makes it (0.0,0.0), but the FITS convention is what it is, and we love and obey standards. The best way to ensure compliance with the standard is to produce a fake image with known star positions and run the code on it.