Tree() length

I made Tree().__len__() to use for finding the number of leafs that
exist on a tree.

libsaria/trees.py

@@ -6,6 +6,12 @@ class Tree(dict):
 	def __init__(self):
 		dict.__init__(self)
 
+	def __len__(self):
+		count = 0;
+		for path in self.walk():
+			count += 1
+		return count
+
 	def __disp__(self, level):
 		return "%s (%s)", (child, self[child].value)