Add parameter to optionally gzip all output fits files

[henryroe]

My preference is to keep all my fits files gzip'd on disk to save disk space.

I created Issue #13 (and pull request #14) to allow for raw fits files in the indata directory to be gzip'd.

It would be great to have a parameter to control the output of plp and optionally gzip all output fits files as well.

The straight-forward part of this is adding to the libs/fits.py to write gzip'd fits files. What I'm less certain of is where the parameter controlling gzip'd vs. not-gzip'd output should go:

• Somehow in to the recipe_log files?
• As a command line flag? e.g.: python ./igr_pipe.py flat 20140316 --gzip-output

If someone tells me the preferred method for passing a parameter to plp, I'll implement it and submit a pull request.

Thanks,
-Henry