Merge pull request #358 from GalSim-developers/#345

#345 - An HST COSMOS correlation function for use in padding COSMOS-derived RealGalaxy objects
ack noticed missing variance dox for get_COSMOS_CorrFunc, after merge of course, fixing quickly on master. Sorry...
made a start on noise whitening...
(#352)
moved docstring additions for things in Noise.h and Noise.cpp from random.py to noise.py in Python layer: seems more natural, also noise.py is now not so short and random.py not so long...
(#352)