Added minimum values and validators for the amplitude and delta parametes
Added minimum values and validators for the amplitude and delta parametes

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