Official logo and README overhaul

[Korijn]

The README needs to be overhauled; focused on getting newcomers up and running quickly, and helping them resolve any issues setting up. Of course, this can all be part of the documentation, but the README is a sort of "business card". So it needs a pretty logo, badges, and a webp animation that shows off what pygfx is capable of.

Here is our new logo:

This zip file contains a ton of variations on it:
PyGFX_LogoSet.zip