add definition of the AST for the cd command

The AST enables us to represent commands via structs. These will hold
all the information about the command for an interpreter.

Change-Id: I4ab45865d5b71c2e1695b1c7c82660fd146da627
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8cd1aa9..ad8c3c2 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -51,6 +51,7 @@
     src/main.cpp
     src/CTree.cpp
     src/CParser.cpp
+    src/ast.cpp
     )
 
 add_executable(netconf-cli ${netconf-cli_SRCS})