Permit any callable, not just a function, for format
Permit any callable, not just a function, for format

For instance, a class that implements a `__call__` method is also fine.

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