Threads have been introduced in ptpython 3.0.11 ; the input UI runs in a
separate thread. In addition, default completers also run in threads.
This is a problem for us, for 3 reasons:

    - aiogevent sets up a gevent backend for asyncio, as a result operations that
      run in an executor for example are executing in different gevent hubs ; it
      is not safe to share gevent objects between threads
    - when showing results, code is called from another thread
        - as we display `__info__` strings which can communicate via sockets etc,
        we get "cannot switch to a different thread" error since sockets cannot be
        shared between gevent loops in different threads
    - when executing properties and methods discovery for completion, there is a
      possibility of communication via sockets, to get redis keys (for example),
      this cannot be executed in another thread (same reason as above)

This code overwrites ._create_buffer(), .read() and .run_async() in order to provide
versions with no threads ; in our case there is no blocking because we use
aiogevent for asyncio + monkey-patched Python so we can avoid threads.
    completely.