ActionParameter helps you move all your parameter's logic from controllers into it's own class. This way you'll keep your controllers dry and they'll be easier to test.
Great work on this.
This is simple a suggestion instead of an issue.
My suggestion is to add on the examples the before and after of using this gem.
Something like "You use to do ... but with action_parameter you simply have to ..."
In that way it is easier to understand how this gems really works.
Sorry for not sending a pull request on this(which I would love to do), but I'm really bussy right now.