Fixed multiproc and cleanup

I fixed the multiprocessing stuff so that if the number of processors is 1, it
will not use multiprocessing.Pool, which doesn't work in the interactive
session. Also added the number of processors as a command line argument.

Cleaned up a bunch of stuff having to do with integrations. Don't need to
return anything from the integration function.
Added a simulated GCMS to the integration

I realized that I wanted a simulated GCMS based on integrations, so I added
that to the AIAFile.integration function.

Updated calibration.py and data.py to reflect the above change.
Generate plot of internal standard

When doing an internal standard calibration, I added some code to plot the
internal standard peak and the corresponding fit. That way I can check that it
is getting fit correctly.