Multiprocessing in sig_severalmasspoints

Hi Noel,

Could you push this into you repository ?
As you suggested, I implemented a multiprocessing treatment of the pvalue computation. It works like a charm, and takes ~6-7 minutes to converge for the CB 8 TeV.

I also modified the 'constructor' of runSig to reduce the verbosity (printing of all the parameters) of the pvalue calculation.

Cheers,
Quentin