adding hooks for preload screen issue #317, needs formatting and ability to subclass/modify before adding
Merge branch 'master' of github.com:lmccart/p5.js
Handle resize events and allow canvas resizing

* Added windowResized callback
* Made the createCanvas keep an id around so we can find user created canvases later
* Changed createCanvas to resize the graphics object if it already exists
* Added a resizeCanvas method
* Added resize to the p5.Graphics object
* (Minor) My editor stripped whitespace on some lines. It was only a small subset so I believe your standard is to strip them so I left it in.