code: function(obj, keys) {
      var newObj = {};
      for (var prop in obj) {
        if (keys.indexOf(prop) === -1) {
          newObj[prop] = obj[prop];
        }
      }
      return newObj;
    }
docs: Makes a shallow copy of `obj` (like `_extend`) but filters its properties based on a list of `keys` to omit.
  The inverse of `_pick`.
  
  @returns A new filtered object.
  @private