save methods

Adding three methods to the API:

* saveTable()
* saveJSON()
* saveStrings()

As part of this process, I also worked on the PrintWriter class, which formats output, the writeFile() method, which prompts download, and some more helper methods like escape(). I hope these'll come in handy down the line !
can this be attached to the main object like the other classes you've made for sound and other p5 classes?
eg ```p5.PrintWriter = function(name) {```