Decide on content of H4 ramp time cards.

What does Subaru want for the H4RG ramp time cards? The PHDU can only know about the starting time stamp: should it only have MJD-STR cards (using MJD as the example one of MJD,HST,UT,LST)? Could also make the case for using straight MJD cards instead of MJD-STR cards.

The per-read HDUs can obviously know about their start and end times; should they each have MJD-STR, MJD, MJD-END or is that silly and/or conflicting? Note that the times themselves would be boringly predictable: they will be calculated from the ramp start and the ramp time, and not by asking a clock for the time.

Do we want -END cards for the entire ramp? Would that go into the last read's HDU, or would we add a post-ramp HDU for summary/"at-end" cards?