split ast definitions into more files

Also move pathToString definitions into the new files

Change-Id: I08b92ed108392825ec87af1f2b8a49205265dd47
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9e21d4f..4ec7140 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -57,7 +57,8 @@
 set(parser_SRCS
     src/schema.cpp
     src/parser.cpp
-    src/ast.cpp
+    src/ast_commands.cpp
+    src/ast_path.cpp
     src/utils.cpp
     src/parser_context.cpp
     src/interpreter.cpp