Don't publicly document Sprite constructor

[toolness]

This is an attempt to fix #63.

It's a bit tricky, though: documenting the constructor as @private actually ends up marking the entire class as private, which prevents Sprite.html from being generated entirely! 😞

On top of that, it seemed impossible to add notes to the constructor advising users to use createSprite() instead: any documentation I tried adding either didn't show up, or it showed up in the class documentation, which is located waaaaay above the constructor. Meaning that users scrolling down to read the constructor docs likely wouldn't see the note about using createSprite.

So instead, I opted to simply remove the documentation for the constructor. It's still accessible from code, obviously, but it's undocumented now. Which IMO is probably a good thing, as it makes it that much less likely for users to accidentally use the constructor and then get confused when their sprite doesn't show up. However, it also means that there's no comments which help readers of the code understand what arguments the constructor takes. Suggestions welcome!

Oh, another thing: I'm using YUIDoc's crossLink helper here to directly link to the documentation for createSprite, but it's actually semi-broken at present due to kevinlacotaco/yuidoc-bootstrap-theme#24. Hopefully we can fix that soon, but at least for now it takes the user to the proper page, where they can manually find the createSprite method on their own.

[islemaster]

Could move this documentation of parameter types into a plain-old-JS-comment just inside the function, to preserve the documentation for devs without mucking up the generated documentation.

[toolness]

That's a good idea... something like this maybe?

// For details on why these docs aren't in a YUIDoc comment block, see:
// 
// https://github.com/molleindustria/p5.play/pull/67
//
// @param {Number} x Initial x coordinate
// @param {Number} y Initial y coordinate
// @param {Number} width Width of the placeholder rectangle and of the
//                       collider until an image or new collider are set
// @param {Number} height Height of the placeholder rectangle and of the
//                        collider until an image or new collider are set

[quinton-ashley]

Undid this change since the move to ES6 classes requires it. Using the Sprite constructor is now equivalent to calling createSprite in v2.2.9