[Solution] DayRange (#92)

Hello,

this is my little solution. I created a second one, that’s faster than
this, but it looks like C, so I don’t post it.

IMHO a cleaner code is more valuable than .3s difference when processing
1M arrays. That doesn’t mean my code is clean.

Someone in #ruby-de @ freenode made a similar but nicer code, maybe I
convince him to submit his solution too.

Happy Quizzing
Robert