Add help command

Change-Id: Ifbda5a7aafefe396854c00add315fb7a67d4fb26
diff --git a/src/ast_handlers.hpp b/src/ast_handlers.hpp
index 7eed8be..96ccc53 100644
--- a/src/ast_handlers.hpp
+++ b/src/ast_handlers.hpp
@@ -458,6 +458,8 @@
 
 struct commit_class;
 
+struct help_class;
+
 struct get_class;
 
 struct command_class {