MINOR: lua: add AppletHTTP class and service

This class is used by Lua code for running as an applet called in HTTP mode
It defines also the associated lua service
diff --git a/include/types/hlua.h b/include/types/hlua.h
index eccfc6c..ac56c2a 100644
--- a/include/types/hlua.h
+++ b/include/types/hlua.h
@@ -18,6 +18,7 @@
 #define CLASS_HTTP         "HTTP"
 #define CLASS_MAP          "Map"
 #define CLASS_APPLET_TCP   "AppletTCP"
+#define CLASS_APPLET_HTTP  "AppletHTTP"
 
 struct stream;