split ast definitions into more files

Also move pathToString definitions into the new files

Change-Id: I08b92ed108392825ec87af1f2b8a49205265dd47
diff --git a/src/grammars.hpp b/src/grammars.hpp
index 9e4ea35..937fd3c 100644
--- a/src/grammars.hpp
+++ b/src/grammars.hpp
@@ -8,7 +8,7 @@
 
 #pragma once
 
-#include "ast.hpp"
+#include "ast_commands.hpp"
 #include "ast_handlers.hpp"