Update mruby doc

doc/nghttpx.h2r

@@ -185,23 +185,20 @@ server.  These hooks allows users to modify header fields, or common
 HTTP variables, like authority or request path, and even return custom
 response without forwarding request to backend servers.
 
-To set request phase hook, use :option:`--request-phase-file` option.
-To set response phase hook, use :option:`--response-phase-file`
-option.
-
-For request and response phase hook, user calls :rb:meth:`Nghttpx.run`
-with block.  The :rb:class:`Nghttpx::Env` is passed to the block.
-User can can access :rb:class:`Nghttpx::Request` and
-:rb:class:`Nghttpx::Response` objects via :rb:attr:`Nghttpx::Env#req`
-and :rb:attr:`Nghttpx::Env#resp` respectively.
+To specify mruby script file, use :option:`--mruby-file` option.  The
+script will be evaluated once per thread on startup, and it must
+instantiate object and evaluate it as the return value (e.g.,
+``App.new``).  This object is called app object.  If app object
+defines ``on_req`` method, it is called with :rb:class:`Nghttpx::Env`
+object on request hook.  Similarly, if app object defines ``on_resp``
+method, it is called with :rb:class:`Nghttpx::Env` object on response
+hook.  For each method invocation, user can can access
+:rb:class:`Nghttpx::Request` and :rb:class:`Nghttpx::Response` objects
+via :rb:attr:`Nghttpx::Env#req` and :rb:attr:`Nghttpx::Env#resp`
+respectively.
 
 .. rb:module:: Nghttpx
 
-.. rb:classmethod:: run(&block)
-
-    Run request or response phase hook with given *block*.
-    :rb:class:`Nghttpx::Env` object is passed to the given block.
-
 .. rb:const:: REQUEST_PHASE
 
     Constant to represent request phase.
@@ -379,19 +376,23 @@ Modify requet path:
 
 .. code-block:: ruby
 
-    Nghttpx.run do |env|
+    class App
+      def on_req(env)
         env.req.path = "/apps#{env.req.path}"
       end
+    end
 
-Note that the file containing the above script must be set with
-:option:`--request-phase-file` option since we modify request path.
+    App.new
+
+Don't forget to instantiate and evaluate object at the last line.
 
 Restrict permission of viewing a content to a specific client
 addresses:
 
 .. code-block:: ruby
 
-    Nghttpx.run do |env|
+    class App
+      def on_req(env)
         allowed_clients = ["127.0.0.1", "::1"]
 
         if env.req.path.start_with?("/log/") &&
@@ -400,6 +401,9 @@ addresses:
           env.resp.return "permission denied"
         end
       end
+    end
+
+    App.new
 
 SEE ALSO
 --------