Allow for simple scenes

[iros]

Allow users to define enter only scenes by bypassing having to set an object with an enter function like so:

var walkthrough = new Miso.Scene({
  initial : 'one',
  scenes : {
    one : function() {
      // do something
      console.log("Doing task one.");
    },
    two : function() {
      // do something else
      console.log("Doing task two.");
    }
    three : {}
  }
});