Clarify and document required/supported libraries

at least until #490 is completed.

consumers can decide whether or not to include it in their app depending on the version of jquery they are using

Also, use a greater than instead of a tilde for defining the jquery requirement.
> This pollutes global, am I right? It defines jQuery.browser and Rangy. We shouldn't do that to our users.

How does us packaging it pollute global any more than them including it on the page? They're 100% equivalent from that standpoint.

> But we don't have to do that, so why bother?

Because we like our users, we want to make their lives easier wherever possible and we don't want to spend time responding to tickets with questions about exactly which versions of all of our required libraries they're using.

The trade-off is not about global pollution (that's equivalent). It's about convenience versus control. For the vast majority of our users who just want a working editor, bundling requirements maximizes convenience. For the minority of our users who want to tweak things, they can make their own custom builds that includes/excludes whatever they would like. Ideally, we'd have a [badass build customization system](http://getbootstrap.com/customize/) that would make it trivial for folks to do custom builds, but the value in something like that is much lower than the tickets blocking 1.0.0, imo.

Thoughts?