remove unicode gem dependency

Turns out the unicode normalization functionality from it we were using
has been in ActiveSupport since 3.0. So un-needed, and we can simplify
things substantially without the unicode gem -- which only worked on
MRI anyway, maybe had problems in ruby 2.0, and required alternates on
jruby etc. Much simpler now, just use ActiveSupport!
Merge pull request #632 from jrochkind/remove_unicode_gem

remove unicode gem dependency