Add traits plugin

[ClickerMonkey]

Adds an array of objects to the prototype of the given Model. If a function is given it is invoked with the Model and options expecting an object to be returned.

Example:

function TraitGenerator( model, options ) {
  return {
    traitFunction: function() {
      // this = model instance
    }
  }
}

var MyTrait = {
  sharedFunction: function() {
    this.set({done: true, done_at: Rekord.now()});
    return this.save();
  }
};

var Task = Rekord({
  name: 'task',
  fields: ['name', 'done', 'done_at'],
  traits: [MyTrait, TraitGenerator]
});