Add run_forever().

pep-3156.txt

@@ -171,7 +171,7 @@ A conforming event loop object has the following methods:
   Note: if you schedule a call with ``call_repeatedly()``, ``run()``
   will not exit until you cancel it.
 
-  TBD: A method to run the loop forever, i.e. until ``stop()`` is called?
+  TBD: How many variants of this do we really need?
 
 - ``stop()``.  Stops the event loop as soon as it is convenient.  It
   is fine to restart the loop with ``run()`` (or one of its variants)
@@ -182,6 +182,8 @@ A conforming event loop object has the following methods:
   called must still be run, but callbacks scheduled after it is called
   (or scheduled to be run later) will not be run.
 
+- ``run_forever()``.  Runs the event loop until ``stop()`` is called.
+
 - ``run_until_complete(future, timeout=None)``.  Runs the event loop
   until the Future is done.  If a timeout is given, it waits at most
   that long.  If the Future is done, its result is returned, or its