I find using if..else easier to understand than unless with early return

Since we are 'taking in', using the negative logic predicate 'unless yield(elem)' is hard to follow, because that particular elem is the one we are taking in.
Merge pull request #14 from 404pnf/patch-1

I find using if..else easier to understand than unless with early return
Release 0.0.8
+ Add String#ascii_only & #ascii_only!
* Wrap spec for `ascii_only` in condition so it does not run on JRuby until `1.7.5`
Merge pull request #13 from PikachuEXE/feature/string-unicode

+ Add String#ascii_only & #ascii_only!
Mention String#ascii_only in the README
Don't iterate longer than necessary
Merge pull request #16 from bquorning/performance

Performance