v0.2.0

• Added an explicit 'a lifetime to most types, representing the lifetime of the Automaton. This allows the creation of Modes that hold onto references, e.g.

  struct SomeMode<'a> {
      reference : &'a mut SomeType,
  }
  
  impl<'a> Mode<'a> for SomeMode<'a> {
      // ...
  }

• Added a new TransitionBox<'a, T> type alias to clean up the Mode interface a bit.