Adds aurora.psh example

[ruifonseca]

This example builds on mandelbrot.psh.
It's called Aurora due to the color palette used and the effect it produces.

I wanted to play with actors, and the Mandelbrot example takes ~2.5 seconds on my laptop.
This brings it down to ~700ms.

[maximecb]

Thanks Rui!

Suggestions: I think it might run faster if you render entire rows of pixels at a time into a ByteArray. There is now an easy ByteArray.set_u32(i) method which can allow you to set the color of a pixel by index in a row of pixels. You can also use the memcpy() method in the main thread to copy rows of pixels an entire row at a time into the final image which is really fast (throughput is gigabytes per second).

You could also try adding some shades or purple in there as well :)