primitives/Delay_ms: .clear() clears Event.

Author: peterhinch

v3/docs/TUTORIAL.md

@@ -1212,6 +1212,7 @@ Synchronous methods:
  6. `callback` args `func=None`, `args=()`. Allows the callable and its args to
  be assigned, reassigned or disabled at run time.
  7. `deinit` No args. Cancels the running task. See [Object scope](./TUTORIAL.md#44-object-scope).
+ 8. `clear` No args. Clears the `Event` decribed in `wait` below.
 
 Asynchronous method:
  1. `wait` One or more tasks may wait on a `Delay_ms` instance. Pause until the
@@ -1251,6 +1252,7 @@ from primitives.delay_ms import Delay_ms
 
 async def foo(n, d):
     await d.wait()
+    d.clear()  # Task waiting on the Event must clear it
     print('Done in foo no.', n)
 
 async def my_app():

v3/primitives/delay_ms.py

@@ -26,6 +26,7 @@ def __init__(self, func=None, args=(), duration=1000):
         self._trig = asyncio.ThreadSafeFlag()
         self._tout = asyncio.Event()  # Timeout event
         self.wait = self._tout.wait  # Allow: await wait_ms.wait()
+        self.clear = self._tout.clear
         self._ttask = self._fake  # Timer task
         self._mtask = asyncio.create_task(self._run()) #Main task
 
@@ -40,7 +41,6 @@ async def _run(self):
     async def _timer(self, dt):
         await asyncio.sleep_ms(dt)
         self._tout.set()  # Only gets here if not cancelled.
-        self._tout.clear()
         self._busy = False
         if self._func is not None:
             self._retn = launch(self._func, self._args)