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 !
I think this should return the p5.PrintWriter object here rather than just the name right?
also if it's called again and a pWriter with that name already exists maybe it should return the existing writer? not sure about this one...