Removed dependency on ActiveSupport, because it's dependencies were conflicting
with the requirements of my Sinatra project:
  > $ bundle install
  > Bundler could not find compatible versions for gem "rack":
  >   In Gemfile:
  >     mongoid-encrypted-fields (>= 0) ruby depends on
  >       rack (~> 1.4.5) ruby
  >
  >     unicorn (>= 0) ruby depends on
  >       rack (1.5.1)
ActiveSupport concern is nothing but a syntactic sugar on standard Ruby meta
techniques.
No code change. Fixing indentation, removed commented out code, and annotating
end tags for clarity.