code: function _initCollections() {
      if (!this._collections) {
        return;
      }
  
      for (var coll in this._collections) {
        this[coll] = new this._collections[coll](null, { parent: this, parse: true });
      }
    }
docs: Initializes collections as type defined in model definition.
  @method _initCollections
  @memberof JSONAPIModel
  @instance
  @private
  @returns {Object} An instance of the collection type