Tweak events example

[almarklein]

Make it more like the renderview event tester at https://pygfx.org/renderview/tester.html

[Vipitis]

Hey, my opinion:
These examples will be looked at by people new to rendercanvas as a reference and tutorial. Which includes absolute beginners too.
As such it might look too daunting at first sight compared to the minimal 20 line version it was before. Perhaps a few comments (to explain how easy it is to setup events; and which parts are just to make it fancy) as well as links to the docs/event spec would help.

[almarklein]

Good point! This example is indeed mostly meant for testing purposes. Let's prefix it as such, and keep a simpler version similar to what we had before.