Jupyter-rfb

What's Changed

* Better performance by avoiding base64-encoding image data by manzt in https://github.com/vispy/jupyter_rfb/pull/76
* Update event spec by almarklein in https://github.com/vispy/jupyter_rfb/pull/78
* Update examples to new version of pygfx by almarklein in https://github.com/vispy/jupyter_rfb/pull/80
* Add grid example by almarklein in https://github.com/vispy/jupyter_rfb/pull/82

* Drop python 3.7 and 3.8 by kushalkolar in https://github.com/vispy/jupyter_rfb/pull/71
* Restrict widget size by almarklein in https://github.com/vispy/jupyter_rfb/pull/70

* Fix that `jupyter_rfb` was broken for the latest ipywidgets by skapin in https://github.com/vispy/jupyter_rfb/pull/64
* Make things work on other notebook implementations by almarklein in https://github.com/vispy/jupyter_rfb/pull/67
* Update examples by almarklein in https://github.com/vispy/jupyter_rfb/pull/66

* Docs on wheel event.
* Pin versions to stricter upstream libs because the new ipywidgets requires changes.

* Improved event specification (docs).
* Reduce throttle timeout for wheel events.
* Prevent the widget from grabbing wheel events if it just passes by during a scroll.
* The wheel event magnitude is tweaked for better consistency.

This release focuses on performance improvements:

* The widget only performs draws if it has views that are visible in the browser. So if an animated widget scrolls out of the viewport, it won't consume CPU.
* The widget now uses JPEG encoding for the images, which is much faster to encode, and faster to send over (smaller payload). There is also a new `quality` trait to control the quality. At the end of an interaction the widget always sends a lossless PNG so the static image always looks perfect.

Further:

* Improvements to docs.
* Improvements to contributor guide.