code: function off(name, hdl) {
          var list = eventHandlers[name];
          if ( list ) {
              if ( hdl ) {
                  eventHandlers[name] = _.difference(list, [hdl]);
              }
              else {
                  delete eventHandlers[name];
              }
          }
          return this;
      }
docs: ------------------------------------------------------------------------- 
  Unbind an event listener or a list of event listeners from the model.
  
  @param (string)   name      - event name    - optional
  @param (function) hdl       - event handler - optional
  
  Usage:
  .off(name, hdl) - remove the hdl from event name
  .off(name)      - remove all listeners for event name