Rendercanvas

This release marks a big step with regards to support for async:

* Refactor to go async by almarklein in https://github.com/pygfx/rendercanvas/pull/41
* A bit more docs on async by almarklein in https://github.com/pygfx/rendercanvas/pull/44

Further improvements:

* Handle ctrl-c by almarklein in https://github.com/pygfx/rendercanvas/pull/25
* Add backend overview to docs by almarklein in https://github.com/pygfx/rendercanvas/pull/43
* Fix rendering via bitmap adapter by almarklein in https://github.com/pygfx/rendercanvas/pull/45
* Run examples on ci by almarklein in https://github.com/pygfx/rendercanvas/pull/23

Changes to the API:

* Rename `is_closed()` to `get_closed()` by almarklein in https://github.com/pygfx/rendercanvas/pull/26
* Remove `run` function by almarklein in https://github.com/pygfx/rendercanvas/pull/42


**Full Changelog**: https://github.com/pygfx/rendercanvas/compare/v1.0.0...v2.0.0

This marks the first release since this repo was rolled out of [wgpu-py](https://github.com/pygfx/wgpu-py). Compared to the version in wgpu-py, this code underwent the following changes:

* Obvious renaming, e.g. `WgpuCanvas` -> `RenderCanvas`.
* The `canvas.get_context()` must be called with `canvas.get_context("wgpu")`.
* The above means that the canvas can also be used by other rendering systems.
* We provide a bitmap-based context `canvas.get_context("bitmap")` out of the box.
* Add backends for qt libs, e.g. `from rendercanvas.pyside6 import RenderCanvas`.
* New scheduling system that is implemented generally instead of separate for each backend, and is generally better in several ways.
* Multiple different update modes are supported.
* The backend system is much better defined, and a few bugs were fixed in this process.
* Don't call `asyncio.get_event_loop()`, because its deprecated now.