made http and socks sub-plugins from proxy

lib/httpx/plugins/proxy.rb

@@ -5,11 +5,6 @@ require "forwardable"
 module HTTPX
   module Plugins
     module Proxy
-      def self.configure(*)
-        require "httpx/plugins/proxy/http"
-        require "httpx/plugins/proxy/socks"
-      end
-
       class Parameters
         extend Registry
 
@@ -72,6 +67,11 @@ module HTTPX
           end
         end
       end
+ 
+      def self.configure(klass, *)
+        klass.plugin(:"proxy/http")
+        klass.plugin(:"proxy/socks")
+      end
     end
     register_plugin :proxy, Proxy
   end

lib/httpx/plugins/proxy/http.rb

@@ -116,5 +116,6 @@ module HTTPX
         Parameters.register("http", HTTPProxyChannel)
       end 
     end
+    register_plugin :"proxy/http", Proxy::HTTP
   end
 end

lib/httpx/plugins/proxy/socks.rb

@@ -109,6 +109,7 @@ module HTTPX
         end
       end
     end
+    register_plugin :"proxy/socks", Proxy::Socks
   end
 end