Make it easier to subclass Table
Make it easier to subclass Table

Before this patch, every subclass needed to implemented its own
_new_from_slice.

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