def helper(name, &block)
      (@setups << Helper.new(name, &block)).last
    end
Helpers are essentially methods accessible within a situation.

They're not setup methods, but can be called from setups or from assetions. Each time called, the
helper will be evaluated. It's not currently memoized.

context "A string" do
helper(:foo) { "bar" }
asserts("a foo") { foo }.equals("bar")
end

@param [String, Symbol] name the name of the helper
@return [Riot::Helper]