upgrade to async syntax

samples/async/aio_web.py

@@ -14,17 +14,16 @@
 def index(request):
     return web.Response(body=b'<h1>Index</h1>')
 
-def hello(request):
-    yield from asyncio.sleep(0.5)
+async def hello(request):
+    await asyncio.sleep(0.5)
     text = '<h1>hello, %s!</h1>' % request.match_info['name']
     return web.Response(body=text.encode('utf-8'))
 
-@asyncio.coroutine
-def init(loop):
+async def init(loop):
     app = web.Application(loop=loop)
     app.router.add_route('GET', '/', index)
     app.router.add_route('GET', '/hello/{name}', hello)
-    srv = yield from loop.create_server(app.make_handler(), '127.0.0.1', 8000)
+    srv = await loop.create_server(app.make_handler(), '127.0.0.1', 8000)
     print('Server started at http://127.0.0.1:8000...')
     return srv