Expose msg stream types at top level

tractor/__init__.py

@@ -5,7 +5,13 @@ tractor: An actor model micro-framework built on
 from trio import MultiError
 
 from ._ipc import Channel
-from ._streaming import Context, stream, context
+from ._streaming import (
+    Context,
+    ReceiveMsgStream,
+    MsgStream,
+    stream,
+    context,
+)
 from ._discovery import get_arbiter, find_actor, wait_for_actor
 from ._trionics import open_nursery
 from ._state import current_actor, is_root_process