Add identity engine as the old dry engine

lib/rest-builder.rb

@@ -1,5 +1,6 @@
 
 require 'rest-builder/builder'
+require 'rest-builder/engine/identity'
 
 module RestBuilder
   REQUEST_METHOD   = 'REQUEST_METHOD'

lib/rest-builder/engine/identity.rb

@@ -0,0 +1,11 @@
+
+require 'rest-builder/middleware'
+
+module RestBuilder
+  class Identity
+    include Middleware
+    def call env
+      yield(env)
+    end
+  end
+end

test/engine/test_identity.rb

@@ -0,0 +1,12 @@
+
+require 'rest-builder/test'
+
+describe RestBuilder::Identity do
+  would 'respond basic status, body, and headers' do
+    env = {RestBuilder::REQUEST_PATH => '/path'}
+
+    RestBuilder::Identity.new.call(env) do |result|
+      expect(result).eq(env)
+    end
+  end
+end