new ProxyEngine dispatches to multiple engines; contributed by jason pellerin
new ProxyEngine dispatches to multiple engines; contributed by jason pellerin

Cito/sqlalchemy,zzzeek/sqlalchemy,wujuguang/sqlalchemy,WinterNis/sqlalchemy,elelianghh/sqlalchemy,davidjb/sqlalchemy,wfxiang08/sqlalchemy,sqlalchemy/sqlalchemy,bootandy/sqlalchemy,davidfraser/sqlalchemy,dstufft/sqlalchemy,brianv0/sqlalchemy,Cito/sqlalchemy,sandan/sqlalchemy,276361270/sqlalchemy,WinterNis/sqlalchemy,halfcrazy/sqlalchemy,graingert/sqlalchemy,EvaSDK/sqlalchemy,monetate/sqlalchemy,monetate/sqlalchemy,alex/sqlalchemy,Akrog/sqlalchemy,halfcrazy/sqlalchemy,j5int/sqlalchemy,hsum/sqlalchemy,alex/sqlalchemy,inspirehep/sqlalchemy,hsum/sqlalchemy,wfxiang08/sqlalchemy,EvaSDK/sqlalchemy,olemis/sqlalchemy,j5int/sqlalchemy,pdufour/sqlalchemy,pdufour/sqlalchemy,ThiefMaster/sqlalchemy,276361270/sqlalchemy,davidfraser/sqlalchemy,brianv0/sqlalchemy,sandan/sqlalchemy,alex/sqlalchemy,robin900/sqlalchemy,wujuguang/sqlalchemy,elelianghh/sqlalchemy,graingert/sqlalchemy,epa/sqlalchemy,davidjb/sqlalchemy,olemis/sqlalchemy,bdupharm/sqlalchemy,itkovian/sqlalchemy,Cito/sqlalchemy,ThiefMaster/sqlalchemy,bootandy/sqlalchemy,dstufft/sqlalchemy,robin900/sqlalchemy,inspirehep/sqlalchemy,itkovian/sqlalchemy,Akrog/sqlalchemy,bdupharm/sqlalchemy,epa/sqlalchemy