add support for '*' transition entry

[dawidgorny]

Inspired by a state machine in Unity where you can define transitions from 'Any'. This way you can avoid repetition if there is some set of transitions always available no matter in which state we are.

const machine = nanostate('idle', {
  '_any': { 
    'reset': 'idle'
  },

  // ...

}

Closes #14

[goto-bus-stop]

oops, i still dont have publish access 🙈