HTML5 Required w/ Custom Select

Fixes #1741

This adds support for errors with custom selects. Without this fix, a javascript error will be thrown when the browser can't focus to a `select` element with the attribute of `required`.

Examples and documentation have also been added. This is a work in progress as I'd like to refine the error styling (and settings for it).

![Screen Shot 2013-03-06 at 6 54 27 AM](https://f.cloud.github.com/assets/687594/227192/a0f25d1e-8654-11e2-8680-4f4c933895dc.png)