2-letter ESC with improved behavior

Based upon the behavior that @JobJob created to configure the 2-letter ESC sequence code that I committed up stream, with the help of @mightyguava.

Using code inspired by the lt.objs.style ::font-settings behavior, I've fixed the way that the example text displays, and attempted to clarify (and limit) the actual use of this behavior, instead of offering carte blanche use the behavior to set any option within the CodeMirror.Vim namespace.