Feature Request: Implement the options.filter with support for async/promises

[kolbma]

I don't have the data for the filter in request or response.
There is needed a mongoose query to get this data.
These queries are always async. So I get the result only in a callback or via promise.

No way to return a complete object by the called function:
https://github.com/saintedlama/restify-mongoose/blob/master/index.js#L267
query.where(self.options.filter(req, res));

I've to write a lot of code to get this to work...

This is TypeScript:

function createBookController(req: restify.Request): Promise<restifyMongoose> {
  return controlHelper.dependRequestUser(req)
    .then((user) => {
      const filterobj = { _creator: user._id };
      return createDynfilterFn(filterobj);
    })
    .then((dynfilter) => {
      const bookController = restifyMongoose(Book, {
        filter: dynfilter,
        listProjection: listProjection,
        detailProjection: detailProjection
      });
      log.debug('Created bookController with filter ' + JSON.stringify(dynfilter(undefined, undefined)));
      return bookController;
    });
}

export function query(req: restify.Request, res: restify.Response, next: restify.Next) {
  createBookController(req).then((bookController: restifyMongoose) => {
    bookController.query()(req, res, next);
  });
}

function createDynfilterFn(filterobj: Object): Function {
  const obj = filterobj;
  return (request: restify.Request, response: restify.Response) => {
    return obj;
  };
}

So it would be quite handy if I could give a promise to the filter option.
Or is there another solution?