MINOR: lua: add set/get priv for applets

The applet can't have access to the session private data. This patch
fix this problem. Now an applet can use private data stored by actions
and fecthes.
diff --git a/doc/lua-api/index.rst b/doc/lua-api/index.rst
index 7eef9e4..6adb72e 100644
--- a/doc/lua-api/index.rst
+++ b/doc/lua-api/index.rst
@@ -1596,6 +1596,24 @@
   :param class_AppletHTTP applet: An :ref:`applethttp_class`
   :param string msg: the message to send.
 
+.. js:function:: AppletHTTP.get_priv(applet)
+
+  Return Lua data stored in the current transaction (with the
+  `AppletHTTP.set_priv()`) function. If no data are stored, it returns a nil
+  value.
+
+  :param class_AppletHTTP applet: An :ref:`applethttp_class`
+  :returns: the opaque data previsously stored, or nil if nothing is
+     avalaible.
+
+.. js:function:: AppletHTTP.set_priv(applet, data)
+
+  Store any data in the current HAProxy transaction. This action replace the
+  old stored data.
+
+  :param class_AppletHTTP applet: An :ref:`applethttp_class`
+  :param opaque data: The data which is stored in the transaction.
+
 .. _applettcp_class:
 
 AppletTCP class
@@ -1659,6 +1677,24 @@
   :param class_AppletTCP applet: An :ref:`applettcp_class`
   :param string msg: the message to send.
 
+.. js:function:: AppletTCP.get_priv(applet)
+
+  Return Lua data stored in the current transaction (with the
+  `AppletTCP.set_priv()`) function. If no data are stored, it returns a nil
+  value.
+
+  :param class_AppletTCP applet: An :ref:`applettcp_class`
+  :returns: the opaque data previsously stored, or nil if nothing is
+     avalaible.
+
+.. js:function:: AppletTCP.set_priv(applet, data)
+
+  Store any data in the current HAProxy transaction. This action replace the
+  old stored data.
+
+  :param class_AppletTCP applet: An :ref:`applettcp_class`
+  :param opaque data: The data which is stored in the transaction.
+
 External Lua libraries
 ======================