Healpix Brightness Maps

[taylorbell57]

Presently, Spiderman doesn't allow users to import brightness maps on a healpix grid which would be a super useful feature (likely requiring healpy as a dependency). As of right now I need to convert my healpix grids to spherical harmonics which loses a lot of information, and then spiderman converts those to the concentric-circle grid. If spiderman calculates the latitude-longitude grid somewhere, one could just do an interpolation between the nearest healpy coordinates. spiderman.format_grid() currently does not accept healpix grids as they are not rectangular in latitude-longitude