Aioresult

* Add `py.typed` marker so that type checkers know that type annotations should be used for type checking.

* Add type hints (to the maximum extent reasonably possible), courtesy of TeamSpen210.
* Lazily construct the internal ``Event``, so that ``ResultCapture`` objects can be constructed before the event loop runs (e.g., at global module scope).
* Add nice string representation.

* **Breaking API change:** `ResultCapture.routine` and `ResultCapture.args` are now properties rather than methods (since all they do is directly return an underlying attribute).
* **Breaking API change:** Remove `StartableResultCapture` class; replace with two new elements of functionality:
* Add `**kwargs` to `ResultCapture.run()`, passed through to the underlying async routine. This allows it to be used directly with `trio.Nursery.start()` and `anyio.abc.TaskGroup.start()`.
* Add `ResultCapture.capture_start_and_done_results()`, which allows capturing both the start result and the overall task result as separate `ResultCapture` objects.
* Add some utility functions for waiting for a result: `wait_any()`, `wait_all()` and `results_to_channel()`.
* Allow exceptions to be optionally suppressed from propagating out of `ResultCapture` (but only those of type `Exception`, not those directly derived from `BaseException`).
* Reorganise docs slightly (the tutorial for the main `ResultCapture` functionality is separated from the reference documentation, and the `Future` documentation is moved to its own separate page, and there is an extra page for the new wait functions).

Initial release, with main class ResultCapture, derived class StartableResultCapture, along with Future, and their base class ResultBase.