uasyncio: Allow to override queue length, while setting low default.

The default queue length is set to take under 0.5K RAM on 32-bit system.
A queue length can be passed to get_event_loop() to override it. This
change follows similar change in uasyncio.core.

uasyncio/uasyncio/__init__.py

@@ -6,8 +6,8 @@ from uasyncio.core import *
 
 class EpollEventLoop(EventLoop):
 
-    def __init__(self):
+    def __init__(self, len=42):
-        EventLoop.__init__(self)
+        EventLoop.__init__(self, len)
         self.poller = select.poll()
         self.objmap = {}