astro/fitscube.py: Add "add" and "sub" (subtract) sub-commands
astro/fitscube.py: Add "add" and "sub" (subtract) sub-commands

liweitianux/atoolbox,liweitianux/atoolbox,liweitianux/atoolbox,liweitianux/atoolbox,liweitianux/atoolbox,liweitianux/atoolbox