fix(docs): IO Concurrency for 3.10+

[salticus]

The current example returns errors when run on Python 3.10+.

The new example should work on Python 3.7+.

Details

Missing loop parameter

The function asyncio.create_server lost its loop parameter in Python 3.10 as part of a cleanup of the high-level asyncio api. The function asyncio.create_server has been implicitly retrieving the current loop since Python 3.7.

Python 3.10 Removed

Python 3.10 Changes in the Python API

Missing event loop

The result of asyncio.get_event_loop() appears to be system dependent. The documentation reads

_If there is no running event loop set, the function will return the result of get_event_loop_policy().get_event_loop() call._

_Because this function has rather complex behavior (especially when custom event loop policies are in use), using the get_running_loop() function is preferred to get_event_loop() in coroutines and callbacks._

Since the example did not start an event loop on my system, I took the liberty of writing asyncio.new_event_loop() instead.

Error encountered

Current code returns:

/tmp/io.py:47: DeprecationWarning: There is no current event loop
  loop = asyncio.get_event_loop()

starting server
Task exception was never retrieved

future: <Task finished name='Task-1' coro=<start_server() done, defined at /usr/local/lib/python3.11/asyncio/streams.py:54> exception=TypeError("BaseEventLoop.create_server() got an unexpected keyword argument 'loop'")>
Traceback (most recent call last):
  File "/usr/local/lib/python3.11/asyncio/streams.py", line 85, in start_server
    return await loop.create_server(factory, host, port, **kwds)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: BaseEventLoop.create_server() got an unexpected keyword argument 'loop'

[coveralls]

Coverage: 93.375% (-0.0%) from 93.375% when pulling 2ddd0d8bfe1a0c7d4378a1486739cf9d1e6617d8 on salticus:master into a138cca5f0ef4fbda7dc4071c0e91459032dd3c1 on ReactiveX:master.