Add a single header card (with a comment) to a FITS image header. This is a lot like the wcstools code sethead, except it works more consistently and I can specify a comment for the card.

Usage: hcards_1card.sh PAERR 0.1266 "This is a position error"   
arg1 - name of header card parameter (max 8 chars)
arg2 - value (treated as string) 
arg3 - comment string  

% % hcards_1card.sh --help 
hcards_1card.sh
  Build a FITS header card with a commnet. The value will always be written as 
a right-justified string.