code: public static Iterable<Measurement> filter(Iterable<Measurement> ms, Tag t) {
      return filter(ms, t.key(), t.value());
    }
docs: Returns a new iterable restricted to measurements that match the predicate.
  
  @param ms
  A set of measurements.
  @param t
  The key and value to search for.
  @return
  Measurements matching the predicate.