Create a simple Rails 3 text helper Gem

I've been working on my first Rails 3 plugin, to package up a simple helper function that I like having in the ApplicationHelper of all my apps. You can see the whole code on Github.

Here's my first attempt:

## lib/semantic_id.rb ##

require 'semantic_id/version'

module ::ActionView::Helpers::TextHelper

  def semantic_id
    string = String.new

    case
    when controller.action_name =~ /new|edit/
      string += controller.action_name + "_"
    when controller.action_name =~ /index|create/
      string += controller.controller_name
    else
      string += controller.controller_name.singularize
    end

    string += "_view"
  end

end

Now, this works, but as I understand it this is not the 'Rails 3 Way' of extending ActiveSupport or any other Rails module. I haven't been able to find much documentation on how you're "supposed" to build a Rails 3 gem. I tried following the Rails Guide, but the method given there for adding helpers didn't work, or else I was missing something.

My question is: given the code above as an example of the functionality I'm looking for, how would you turn this into a Rails 3 plugin Gem?

Thanks!