smurf: Handle NDFs that do not have an INSTRUME FITS header
smurf: Ignore any non-printing characters on the command line
ast: New sorting options for KeyMap

The existing AgeUp and AgeDown SortBy options use the age of the value as
the sort key. This means that changing the value associated with an
existing entry will change the position of the entry in the sort order.

The new KeyAgeUp and KeyAgeDown SortBy options use the age of the key
as the sort key. This means that changing the value associated with an
existing entry will NOT change the position of the entry in the sort order.