code: function(name, cb){
                  if(typeof cb === 'function'){
                      events[name] = events[name] || [];
                      events[name].push(cb);
                  }
                  return this;
              }
docs: Attach an handler to an event.
  Calling `on` with the same eventName multiple times add callbacks: they
  will all be executed.
  
  @example aja().on('success', function(res){ console.log('Cool', res);  });
  
  @param {String} name - the name of the event to listen
  @param {Function} cb - the callback to run once the event is triggered
  @returns {Aja} chains