p5:dom:media support for multiple file formats + escaping html in yuidoc descriptions

1. p5dom's createAudio() and createVideo() support multiple src file formats. I think this is an important option for users who want browser compatibility. I'm also including a .webm version of fingers.mov because it's one of the few video formats consistently supported by [Firefox](https://developer.mozilla.org/en-US/docs/Web/HTML/Supported_media_formats).

2. I changed "{{{description}}}" to "{{description}}" in yuidocs, which will escape html in descriptions fields. I did this because I noticed that descriptions with html tags were getting cut off. For example, [createAudio](http://p5js.org/reference/#get/Media/createAudio) gets cut off where I expected to display "\<audio>" as text, [createDiv](http://p5js.org/reference/#get/Manipulate/createDiv) has a div, and [createButton](http://p5js.org/reference/#get/Manipulate/createButton) has a button (which is kind of fun). The only way I found to escape the html was with a space like "< div >". That could be a solution if we will ever want to execute html in the description field. Do we want to be able to do this? I could imagine wanting to include hyperlinks and <em>maybe</em> some formatting... let me know if I should make this an issue rather than a pull request.