code: function normalizeEntities(base, input) {
    if (!input) return;
    if (!Array.isArray(input)) input = [ input ];
  
    return flatten(input).filter(Boolean).map(function (entity) {
      assert(entity.rel, 'sub-entities must have a rel');
  
      var ret = normalizeEntity(base, entity);
      ret.rel = normalizeRel(base, entity.rel);
      if (entity.href) ret.href = normalizeHref(base, entity.href);
  
      return ret;
    });
  }
docs: Takes the `input` entities value and normalizes it into a single array.
  
  @param {String} base  The base URL for this API.
  @param {Mixed} input  The entities value to normalize.
  @return {Array}