MINOR: lua: add class proxy

This class provides the access to the proxy struct, it allows
some manipulations and retrieve informations.
diff --git a/include/types/hlua.h b/include/types/hlua.h
index 34bd648..17cf141 100644
--- a/include/types/hlua.h
+++ b/include/types/hlua.h
@@ -19,6 +19,7 @@
 #define CLASS_MAP          "Map"
 #define CLASS_APPLET_TCP   "AppletTCP"
 #define CLASS_APPLET_HTTP  "AppletHTTP"
+#define CLASS_PROXY        "Proxy"
 
 struct stream;