Allow non-quantity inputs even with input and return units.
Allow non-quantity inputs even with input and return units.

Also enforce explicit multiple input and return units (has to be iterable) if
number larger than 1

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