restructured api_classes, use the same base class

jedi/keywords.py

@@ -35,12 +35,13 @@ def get_operator(string, pos):
 class Keyword(object):
     def __init__(self, name, pos):
         self.name = name
-        self.parent = lambda: None
         self.start_pos = pos
 
-    def get_parent_until(self):
+    def parent(self):
         return builtin.Builtin.scope
 
+    get_parent_until = parent
+
     @property
     def names(self):
         """ For a `parsing.Name` like comparision """