Added support for undocumented WorkspaceEventTypes

"reload", "restore" and "reload" are possible types of the workspace
event. They weren't documented (I will contact the responsible person).
I'm not sure if the "reload" signal can be received, but better be safe
than sorry.

include/i3ipc++/ipc.hpp

@@ -89,6 +89,9 @@ enum class WorkspaceEventType : char {
 	INIT = 'i', ///< Initialized
 	EMPTY = 'e', ///< Became empty
 	URGENT = 'u', ///< Became urgent
+    RENAME = 'r', ///< Renamed
+    RELOAD = 'l', ///< Reloaded
+    RESTORED = 's', ///< Restored
 };
 
 /**