Improve fits2bitmap default output filename generation
Improve fits2bitmap default output filename generation

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