Update io.ascii so fill masking is per-column not per-table
Update io.ascii so fill masking is per-column not per-table

lpsinger/astropy,bsipocz/astropy,pllim/astropy,aleksandr-bakanov/astropy,saimn/astropy,StuartLittlefair/astropy,MSeifert04/astropy,stargaser/astropy,StuartLittlefair/astropy,bsipocz/astropy,stargaser/astropy,mhvk/astropy,pllim/astropy,mhvk/astropy,mhvk/astropy,larrybradley/astropy,larrybradley/astropy,dhomeier/astropy,MSeifert04/astropy,dhomeier/astropy,saimn/astropy,mhvk/astropy,larrybradley/astropy,astropy/astropy,StuartLittlefair/astropy,bsipocz/astropy,saimn/astropy,dhomeier/astropy,MSeifert04/astropy,stargaser/astropy,aleksandr-bakanov/astropy,mhvk/astropy,larrybradley/astropy,pllim/astropy,dhomeier/astropy,saimn/astropy,lpsinger/astropy,astropy/astropy,aleksandr-bakanov/astropy,pllim/astropy,saimn/astropy,lpsinger/astropy,lpsinger/astropy,dhomeier/astropy,pllim/astropy,StuartLittlefair/astropy,astropy/astropy,StuartLittlefair/astropy,stargaser/astropy,bsipocz/astropy,astropy/astropy,aleksandr-bakanov/astropy,MSeifert04/astropy,larrybradley/astropy,astropy/astropy,lpsinger/astropy