Caching of p5.min.js and related files

[limzykenneth]

Following up from https://github.com/processing/p5.js/issues/4716, from what I can see, only the reference and examples currently uses p5.min.js and p5.sound.min.js both of which needs to have their cache updated.

The reference is relatively straightforward with the handlebars helper built to handle this before, the examples however are included as <iframe> which just has a HTML source, updating a versioned hashed of it will be a bit more difficult.