reworking hello p5 examples

A first pass at all the hellop5 examples.  cc @scottgarner re: https://github.com/scottgarner/p5.js-video/issues/19

Some notes:

* Flocking and painting don't seem to be working?  
* Any thoughts / ideas on how to deal with styling for "song" example?
* I think I might further simplify the painting example.

If these seem ok and workable on the site I'll take another pass and add code comments and do general clean-up.