Simplify Sparkles

[samepant]

I cleaned up the sparkle symbol definition and made it use standard transforms and not matrices. I also added a function for generating random sparkles.

It would be nice to have the sparkles not show up on the stone, but I haven't spent any time figuring out that math yet.

[jfschwarz]

Solidity has no trigonometric math, so if we wanna generate the random number from the contract we should simplify it a bit. I've pushed a suggestion, just check if it meets your artistic standards, @samepant, otherwise we can certainly still find ways tune it.

[samepant]

@jfschwarz ya this works great