asyncio: sync with Tulip

- Tulip issue 185: Add a create_task() method to event loops. The create_task()
  method can be overriden in custom event loop to implement their own task
  class. For example, greenio and Pulsar projects use their own task class. The
  create_task() method is now preferred over creating directly task using the
  Task class.
- tests: fix a warning
- fix typo in the name of a test function
- Update AbstractEventLoop: add new event loop methods; update also the unit test

Lib/test/test_asyncio/test_futures.py

@@ -301,12 +301,12 @@ class FutureTests(test_utils.TestCase):
     def test_future_exception_never_retrieved(self, m_log):
         self.loop.set_debug(True)
 
-        def memroy_error():
+        def memory_error():
             try:
                 raise MemoryError()
             except BaseException as exc:
                 return exc
-        exc = memroy_error()
+        exc = memory_error()
 
         future = asyncio.Future(loop=self.loop)
         source_traceback = future._source_traceback