Adding multi-darks --- fitting dark current with multi-dimensional polynomial. This allows the dark current to be a function of temperature, or time since PON. To do this, added new file type, DARK. A DARK file is just like an IMAGE, except that it has a table per FITS file that contains the parameters to use in applying the dark. It's kinda like a FRINGE, but there's only one table per file, instead of one table per extension.