Command-line params plus iteration

Modified `run_cosmics.py` : Now accepts (and requires) command-line parameters for `readnoise`, `iter' and `sigclip`.
File names generated for the output now include the parameters used to distinguish them.

Added script `iter_cosmics.py` : Runs `run_cosmics.py` with different values for iterations (currently set at 0-10) , readnoise (currently 2.5-7.5), and sigclip (currently 0.5 - 6.0). Currently uses file `u2mi0102t_c0m.fits`

Both scripts have been tested.

I am going to go through these scripts again to make sure it is going to do what we want and then am gonna run it for the above settings (should be around 250 images) before I leave at 5. If you could take a look before then and provide comments on any changes if necessary then that would be great. If not will look at the images generated tomorrow morning and let you know and we can tweak params from there.