fixed custom TypeEngine example
fixed custom TypeEngine example

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