added search by URL in vos_catalog and updated doc
added search by URL in vos_catalog and updated doc

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