Allow consumers to define there own way to display readability info

[Richie]

Instead of requiring the internal presentation of readability for encompassing content, allow the consumer to define their own way to present this information.

Consumers could pass in a callback to register for something like a onReadabilityChange event. This payload or data passed along with this event would contain the current/present readability information of the contained content.

To make this a non-breaking transition, would always present the default readability view. If a callback handler it passed, then this rendering would be made inactive, and it would be the responsibility of the consumer to update/render this information. A separate flag controller the rendering of default or not could be done, in case consumers just wanted to listen for the change