updated setup.py to support Cython extensions in-source
updated setup.py to support Cython extensions in-source

kelle/astropy,mhvk/astropy,aleksandr-bakanov/astropy,lpsinger/astropy,DougBurke/astropy,lpsinger/astropy,lpsinger/astropy,DougBurke/astropy,saimn/astropy,saimn/astropy,MSeifert04/astropy,pllim/astropy,bsipocz/astropy,StuartLittlefair/astropy,dhomeier/astropy,tbabej/astropy,astropy/astropy,stargaser/astropy,DougBurke/astropy,bsipocz/astropy,StuartLittlefair/astropy,stargaser/astropy,larrybradley/astropy,stargaser/astropy,saimn/astropy,dhomeier/astropy,aleksandr-bakanov/astropy,pllim/astropy,StuartLittlefair/astropy,AustereCuriosity/astropy,funbaker/astropy,tbabej/astropy,tbabej/astropy,tbabej/astropy,joergdietrich/astropy,joergdietrich/astropy,aleksandr-bakanov/astropy,astropy/astropy,astropy/astropy,mhvk/astropy,funbaker/astropy,funbaker/astropy,pllim/astropy,larrybradley/astropy,lpsinger/astropy,StuartLittlefair/astropy,tbabej/astropy,StuartLittlefair/astropy,saimn/astropy,MSeifert04/astropy,larrybradley/astropy,dhomeier/astropy,stargaser/astropy,joergdietrich/astropy,mhvk/astropy,kelle/astropy,MSeifert04/astropy,pllim/astropy,pllim/astropy,AustereCuriosity/astropy,mhvk/astropy,joergdietrich/astropy,MSeifert04/astropy,aleksandr-bakanov/astropy,AustereCuriosity/astropy,bsipocz/astropy,AustereCuriosity/astropy,dhomeier/astropy,kelle/astropy,larrybradley/astropy,bsipocz/astropy,mhvk/astropy,larrybradley/astropy,AustereCuriosity/astropy,joergdietrich/astropy,lpsinger/astropy,dhomeier/astropy,astropy/astropy,DougBurke/astropy,saimn/astropy,kelle/astropy,astropy/astropy,funbaker/astropy,kelle/astropy