use xattree (#87)

tests still need a bit of reworking but mostly there

Author: wpbonelli

.vscode/launch.json

@@ -10,7 +10,8 @@
             "request": "launch",
             "program": "${file}",
             "console": "integratedTerminal",
-            "purpose": ["debug-test"]
+            "purpose": ["debug-test"],
+            "justMyCode": false
         }
     ]
 }