Fix wrong imports

- "from _compatibility import ..." (not in circular imports)
- "from jedi import builtin" (one of circular imports)
- "api_classes = api.api_classes"
  ("from jedi import api_classes" is not supported)

jedi/keywords.py

@@ -2,7 +2,7 @@ import pydoc
 import keyword
 
 from jedi._compatibility import is_py3k
-from jedi import builtin
+import builtin
 
 try:
     from pydoc_data import topics as pydoc_topics