Updated HACKING doc to include specific PEP8 exclusions.
Updated HACKING doc to include specific PEP8 exclusions.

ddaeschler/pyrax,naemono/pyrax,rackerlabs/heat-pyrax,opsdisk/pyrax,vikomall/pyrax,briancurtin/pyrax,mandx/pyrax,0dataloss/pyrax,roelvv/pyrax,emonty/pyos,pratikmallya/pyrax,EdLeafe/pyrax,rackspace/pyrax,sivel/pyrax