Allow attributes to specify how to be represented in the frame repr
Allow attributes to specify how to be represented in the frame repr

This implements a hook to customise the way an attribute is represented in the
frame repr.

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