Add documentation for delegated methods on Metal

Some of these were specifically mentioned earlier in the Metal docs
(response_body=, content_type=, status=) but were not linked because the
methods were not documented (due to being part of a delegation).

This commit separates all of the delegated methods so that they can be
documented, adds links for the mentioned methods, and additionally
documents two methods on Response that are mentioned in the new Metal
documentation, but were not previously documented.

actionpack/lib/action_controller/metal.rb

@@ -81,15 +81,16 @@ def build_middleware(klass, args, block)
   #
   #     get 'hello', to: HelloController.action(:index)
   #
-  # The `action` method returns a valid Rack application for the Rails router to
+  # The ::action method returns a valid Rack application for the Rails router to
   # dispatch to.
   #
   # ## Rendering Helpers
   #
-  # `ActionController::Metal` by default provides no utilities for rendering
-  # views, partials, or other responses aside from explicitly calling of
-  # `response_body=`, `content_type=`, and `status=`. To add the render helpers
-  # you're used to having in a normal controller, you can do the following:
+  # By default, `ActionController::Metal` provides no utilities for rendering
+  # views, partials, or other responses aside from three low-level setters to modify the
+  # response: #response_body=, #content_type=, and #status=. To add the render
+  # helpers you're used to having in a normal controller, you can do the
+  # following:
   #
   #     class HelloController < ActionController::Metal
   #       include AbstractController::Rendering
@@ -179,8 +180,33 @@ def controller_name
     # Delegates to ActionDispatch::Response#headers.
     delegate :headers, to: "@_response"
 
-    delegate :status=, :location=, :content_type=,
-             :status, :location, :content_type, :media_type, to: "@_response"
+    ##
+    # Delegates to ActionDispatch::Response#status=
+    delegate :status=, to: "@_response"
+
+    ##
+    # Delegates to ActionDispatch::Response#location=
+    delegate :location=, to: "@_response"
+
+    ##
+    # Delegates to ActionDispatch::Response#content_type=
+    delegate :content_type=, to: "@_response"
+
+    ##
+    # Delegates to ActionDispatch::Response#status
+    delegate :status, to: "@_response"
+
+    ##
+    # Delegates to ActionDispatch::Response#location
+    delegate :location, to: "@_response"
+
+    ##
+    # Delegates to ActionDispatch::Response#content_type
+    delegate :content_type, to: "@_response"
+
+    ##
+    # Delegates to ActionDispatch::Response#media_type
+    delegate :media_type, to: "@_response"
 
     def initialize
       @_request = nil
@@ -201,7 +227,7 @@ def params=(val)
 
     alias :response_code :status # :nodoc:
 
-    # Basic url_for that can be overridden for more robust functionality.
+    # Basic `url_for` that can be overridden for more robust functionality.
     def url_for(string)
       string
     end

actionpack/lib/action_dispatch/http/response.rb

@@ -231,6 +231,18 @@ def sending?;   synchronize { @sending };   end
     def committed?; synchronize { @committed }; end
     def sent?;      synchronize { @sent };      end
 
+    ##
+    # :method: location
+    #
+    # Location of the response.
+
+    ##
+    # :method: location=
+    #
+    # :call-seq: location=(location)
+    #
+    # Sets the location of the response
+
     # Sets the HTTP status code.
     def status=(status)
       @status = Rack::Utils.status_code(status)
@@ -241,7 +253,7 @@ def status=(status)
     #
     #     response.content_type = "text/plain"
     #
-    # If a character set has been defined for this response (see charset=) then the
+    # If a character set has been defined for this response (see #charset=) then the
     # character set information will also be included in the content type
     # information.
     def content_type=(content_type)