Struct sorter

internal/header/sort.go:13–16

}

type sorter struct {
	order map[string]int
	kvs   []KeyValues
}

func (s *sorter) Len() int      { return len(s.kvs) }
func (s *sorter) Swap(i, j int) { s.kvs[i], s.kvs[j] = s.kvs[j], s.kvs[i] }