Make "certonly" a synonym for "auth", and document it
Make "certonly" a synonym for "auth", and document it

Closes: #657

dietsche/letsencrypt,DavidGarciaCat/letsencrypt,wteiken/letsencrypt,mitnk/letsencrypt,letsencrypt/letsencrypt,stweil/letsencrypt,goofwear/letsencrypt,lbeltrame/letsencrypt,sjerdo/letsencrypt,thanatos/lets-encrypt-preview,wteiken/letsencrypt,kuba/letsencrypt,martindale/letsencrypt,DavidGarciaCat/letsencrypt,BillKeenan/lets-encrypt-preview,TheBoegl/letsencrypt,martindale/letsencrypt,bsmr-misc-forks/letsencrypt,stweil/letsencrypt,mrb/letsencrypt,mitnk/letsencrypt,thanatos/lets-encrypt-preview,brentdax/letsencrypt,mrb/letsencrypt,Sveder/letsencrypt,twstrike/le_for_patching,piru/letsencrypt,sjerdo/letsencrypt,Sveder/letsencrypt,TheBoegl/letsencrypt,lbeltrame/letsencrypt,xgin/letsencrypt,VladimirTyrin/letsencrypt,jtl999/certbot,kuba/letsencrypt,VladimirTyrin/letsencrypt,letsencrypt/letsencrypt,jsha/letsencrypt,goofwear/letsencrypt,lmcro/letsencrypt,piru/letsencrypt,twstrike/le_for_patching,brentdax/letsencrypt,bsmr-misc-forks/letsencrypt,BillKeenan/lets-encrypt-preview,jsha/letsencrypt,jtl999/certbot,lmcro/letsencrypt,dietsche/letsencrypt,xgin/letsencrypt