Updated docs and UTF-8 capitalization.

Fixed the readme to reflect the new UTF-8 default value.

Also updated the default from "utf-8" to "UTF-8". I've searched for a while to see what that standard on this was, and it looks like it doesn't matter. But as a lot of the other folks have pointed out, the overwhelming majority of code examples and explanations have it capitalized. So lets keep it consistent :)