Modal > next major release

[mjbp]

• Remove support for anchors as toggles? Should really only be buttons, not pseudo buttons
• Remove onClassName option since it's rarely used and is--modal classname for documentElement level className change isn't configurable. Compound selectors mean we don't ever really need to change these classNames.
• Remove delay? Purpose is for doing different animation on show and hide, but in practice it is rarely (never?) used and can be replicated using callback fn
• review focus on open with reference to native dialog behaviour, would it be better to set tab index = -1 on dialog and focus on that than first element, and make first element focus an option?

[sarah-storm]

Should #261 be considered in this one?