started operator overload implementation
started operator overload implementation

alubbock/pysb-legacy,johnbachman/pysb,jmuhlich/pysb,alubbock/pysb,LoLab-VU/pysb,alubbock/pysb-legacy,alubbock/pysb-legacy,spgarbet/pysb,spgarbet/pysb,neurord/pysb,neurord/pysb,neurord/pysb,d-fan/pysb,spgarbet/pysb,alubbock/pysb-legacy,LoLab-VU/pysb,johnbachman/pysb,d-fan/pysb,pysb/pysb,d-fan/pysb