Added GaussHermitePSF; still debugging whether it works
fix index order to match Julien's files
update Gauss Hermite PSF docs
Merge branch 'gauss_hermite_psf' into dev
Checkpoint on initial refactor to legendre xy
Converted PSFs to use Legendre polynomials for xy; updated tests to match change in options
Merge branch 'legendre_xy' into dev; changes PSF format
correct doc about PSF spot reference pixel (corner vs. center)