Add a DelegatePresenter base class

Subclasses of this class can easily delegate presenter methods to a
backing object. A parameter with the same name as the class (e.g.
`product` for `ProductPresenter`) must be passed and its value will
receive delegated calls.

lib/curly.rb

@@ -50,5 +50,6 @@ def self.valid?(template, presenter_class)
 
 require 'curly/compiler'
 require 'curly/presenter'
+require 'curly/delegate_presenter'
 require 'curly/template_handler'
 require 'curly/railtie' if defined?(Rails)

lib/curly/delegate_presenter.rb

@@ -0,0 +1,23 @@
+require 'curly/presenter'
+
+module Curly
+  class DelegatePresenter < Curly::Presenter
+    def self.delegates(*methods)
+      methods.each do |method|
+        class_eval <<-RUBY
+          def #{method}
+            @#{delegatee_name}.#{method}
+          end
+        RUBY
+      end
+    end
+
+    def self.inherited(subclass)
+      self.presented_names += [subclass.delegatee_name]
+    end
+
+    def self.delegatee_name
+      name.split("::").last.underscore.sub(/_presenter$/, "")
+    end
+  end
+end

spec/delegate_presenter_spec.rb

@@ -0,0 +1,14 @@
+describe Curly::DelegatePresenter do
+  class PersonPresenter < Curly::DelegatePresenter
+    delegates :name, :age
+  end
+
+  it "allows exposing methods on the passed object" do
+    context = double(:context)
+    person = double(:person, name: "Jane", age: 25)
+    presenter = PersonPresenter.new(context, person: person)
+
+    expect(presenter.name).to eq "Jane"
+    expect(presenter.age).to eq 25
+  end
+end