Tutorial: improve timeout section.

Author: peterhinch

TUTORIAL.md

@@ -904,7 +904,9 @@ Timeouts are implemented by means of `uasyncio.wait_for()`. This takes as
 arguments a coroutine and a timeout in seconds. If the timeout expires a
 `TimeoutError` will be thrown to the coro in such a way that the next time the
 coro is scheduled for execution the exception will be raised. The coro should
-trap this and quit.
+trap this and quit; alternatively the calling coro should trap and ignore the
+exception. If the exception is not trapped the code will hang: this appears to
+be a bug in `uasyncio` V2.0.
 
 ```python
 import uasyncio as asyncio
@@ -922,6 +924,27 @@ async def foo():
     await asyncio.wait_for(forever(), 5)
     await asyncio.sleep(2)
 
+loop = asyncio.get_event_loop()
+loop.run_until_complete(foo())
+```
+Alternatively:
+```python
+import uasyncio as asyncio
+
+async def forever():
+    print('Starting')
+    while True:
+        await asyncio.sleep_ms(300)
+        print('Got here')
+
+async def foo():
+    try:
+        await asyncio.wait_for(forever(), 5)
+    except asyncio.TimeoutError:
+        pass
+    print('Timeout elapsed.')
+    await asyncio.sleep(2)
+
 loop = asyncio.get_event_loop()
 loop.run_until_complete(foo())
 ```

aswitch.py

@@ -115,7 +115,6 @@ def __call__(self):
         return self.switchstate
 
     async def switchcheck(self):
-        loop = asyncio.get_event_loop()
         while True:
             state = self.pin.value()
             if state != self.switchstate: