Implement readRequiredOption. Fixes #442.
Implement readRequiredOption. Fixes #442.

Also renamed getOption to readOption to better highlight that the function may only be called once to read a certain option.

The dissonance in "required option" is a bit unfortunate, but I didn't find a better name overall that is still consistent with the non-required (erm.. optional) version. Also, adding an additional parameter to getOption/readOption would have been not very beautiful either, because then the boolean return value would be partially redundant.

alphaKAI/vibe.d,schuetzm/vibe.d,DBankov/vibe.d,ColdenCullen/vibe.d,fast4shoot/vibe.d,Yoplitein/vibe.d,etcimon/vibe.0,sigod/vibe.d,dkillebrew/vibe.d,sigod/vibe.d,veelo/vibe.d,etcimon/vibe.d,Kozzi11/vibe.d,nathanchristenson/vibe.d,jkm/vibe.d,Yoplitein/vibe.d,Yoplitein/vibe.d,etcimon/vibe.0,gedaiu/vibe.d,etcimon/vibe.d,rejectedsoftware/vibe.d,machindertechnologies/vibe.d,yannick/vibe.d,AndreyMZ/vibe.d,alphaKAI/vibe.d,Geod24/vibe.d,redstar/vibe.d,nathanchristenson/vibe.d,sigod/vibe.d,chalucha/vibe.d,mfrischknecht/vibe.d,Mihail-K/vibe.d,alphaKAI/vibe.d,nathanchristenson/vibe.d,jkm/vibe.d