clean up mapperextension docs
clean up mapperextension docs

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