add bng parsing support for sites with state *and* bond
add bng parsing support for sites with state *and* bond

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