Add menu select event doc
Change menu to use itemIndex and sectionIndex property names

This frees up the item and section fields to reference objects.
Change menu helper getters to private methods
Add item and section references to menu events
Add a reference to menu to menu events.

Menu events already reference the menu with `this`, but referencing menu
is clearer and is safe from rebinded functions.
Add beta and usability notice
Update menu accessor docs detailing retrieval
Clarify Bluetooth impact in usability notice
Merge branch 'develop'