Various touchups

[FoamyGuy]

Two new examples:

• rainbow_spiral.py plots a spiral around the edges of the matrix using PIL circles along with rainbowio
• quote_scroller.py fetches a quote from the API and scrolls it using PIL to render text and then copy/paste it into the image that gets shown each refresh frame.

Updated the fbmirror examples to accept arguments for matrix size, orientation, and scale for the scaled one.

Added a requirements.txt, and fixed a filepath in the readme.

[FoamyGuy]

Also added an animated gif example that plays nyan cat by default.

[jepler]

I think this is fine but I worry a little about the repetition of the command line flag handling.

https://github.com/hzeller/rpi-rgb-led-matrix/blob/552ef44edf80fd56955c6e87ac322eda44b5f07c/bindings/python/samples/samplebase.py has a way of sharing command line flags settings across multiple examples.

I'm just thinking about how, if you wanted to add support for 5-address panels you'd have to go back and change all the examples one by one.

It's up to you whether you want to do something like this now, or whether you think it's not critical.

[FoamyGuy]

Thank you. I'm going to merge it as-is for now so that I can get the new examples embedded into the learn guide.

I will add it to my list to come back and change them to use argparse though, I agree that it will be a nicer solution. I always forget of it's existence and my brain tries to jump straight from argv index access to full Click CLI app which I thought was overkill for this.