checkpoint
Committing test code
Add smaller version of psf-spot.fits
Fix PSF x/y copy when result is a scalar
Fixed psf.xyrange
Even if spot is off CCD, the returned psf should be 2D
fix test_project22
fix psf.xyrange again
All PSF tests pass
Fix reading input spectra from binary tables with 2D flux and 2D wavelength
Add support for photons/A/arcsec^2
Merge branch 'add_tests' into dev.  Unit tests are useful, even if they
are a pain to write...