code: function listFeatures(call) {
    var lo = call.request.lo;
    var hi = call.request.hi;
    var left = _.min([lo.longitude, hi.longitude]);
    var right = _.max([lo.longitude, hi.longitude]);
    var top = _.max([lo.latitude, hi.latitude]);
    var bottom = _.min([lo.latitude, hi.latitude]);
    // For each feature, check if it is in the given bounding box
    _.each(feature_list, function(feature) {
      if (feature.name === '') {
        return;
      }
      if (feature.location.longitude >= left &&
          feature.location.longitude <= right &&
          feature.location.latitude >= bottom &&
          feature.location.latitude <= top) {
        call.write(feature);
      }
    });
    call.end();
  }
docs: listFeatures request handler. Gets a request with two points, and responds
  with a stream of all features in the bounding box defined by those points.
  @param {Writable} call Writable stream for responses with an additional
  request property for the request value.