Automatically generate cassette names from function names. Add

`path_transformer` and `func_path_generator`. Closes #151.

vcr/util.py

@@ -0,0 +1,16 @@
+def partition_dict(predicate, dictionary):
+    true_dict = {}
+    false_dict = {}
+    for key, value in dictionary.items():
+        this_dict = true_dict if predicate(key, value) else false_dict
+        this_dict[key] = value
+    return true_dict, false_dict
+
+
+def compose(*functions):
+    def composed(incoming):
+        res = incoming
+        for function in functions[::-1]:
+            res = function(res)
+        return res
+    return composed