Added preliminary support for inheritance.
Added preliminary support for inheritance.

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