Add back get_vars() to Hierarchy

This adds back a get_vars() method to the Hierarchy class which was
removed in 3f5d98e.

Author: levens

README.md

@@ -65,7 +65,7 @@ Explore variable hierarchies:
 ```python
 ldb.tree
 print(dir(ldb.tree))
-print(ldb.tree.LHC.Collimators.BPM.bpmColl._get_vars())
+print(ldb.tree.LHC.Collimators.BPM.bpmColl.get_vars())
 ```
 
 Get data for a particular LHC fill:

pytimber/pytimber.py

@@ -601,3 +601,6 @@ def _get_vars(self):
             return vvv.toString()[1:-1].split(', ')
         else:
             return []
+
+    def get_vars(self):
+        return self._get_vars()