Define AGCC files for display while guiding

Besides the to-be-archived PFSD guider files and the strange hex image for the Mitsubishi displays, we need to define the files made specifically for displaying while guiding. It turns out that the mechanism for doing this is new at Subaru, so this is a white-sheet design – we should be able to design something which works well for both Subaru and PFS, and it will be collaboratively designed.

A brief discussion led to a few starting suggestions:

• N (6) HDUs for the images
• zero-ed out background. RICE compression. Or maybe in this case HCOMP?
• display scaling parameters in the headers, as well as the WCS.
• a binary table with object and offset properties, good enough for useful annotations.
• either HDU cards or a binary table for the final guiding/focus.
• filename is not bound to the PFS visit
• file is not expected to be used for anything but live display.

 Even though this is purely intended for observing, since it is a published interface I'm putting this ticket in DAMD.