0.4.0

Changed

• Replaced FirstResponderStateChangeHandler typealias with a real type that
  wraps a change handler closure.
• Replaced FirstResponderState with a single boolean value to represent the
  first responder state.

Added

• The ability to easily update external state when the first responder state
  changes using FirstResponderStateChangeHandler.updates($someBinding).
• Easily animate first responder state changes using the .animation() modifier
  on FirstResponderStateChangeHandler
• FirstResponderStateChangeHandler can also be given closures for custom
  control over whether or not the text field should become or resign first
  responder, hooking into the shouldBeginEditing and shouldEndEditing
  delegate methods.