code: function delById(req, res, next) {
    res.__apiMethod = 'delete';
    var self = this;
    var id = req.params.id;
    var filter = this.option('delete', 'filter');
    if (filter instanceof Function) filter = filter.call(this, req);
    var query = extend({_id: id}, filter);
    this.model.remove(query).exec(function(err, affected) {
      if (err) return next(err);
      if (affected.result.n == 0) {
        return next(new ModelAPIError(
          404, `The ${self.nameSingle} was not found by ${id}`
        ));
      }
      res.status(200);
      return res.json({});
    });
  }
docs: delById - controller that deletes a model instance
  
  @param  {express.Request}  req        the http(s) request
  @param  {express.Response} res        the http(s) response
  @param  {Function}         next       the callback should be called if controller fails
  
  @memberof ModelAPIRouter