code: func (h Headers) Index(k string) int {
  	r := -1
  	for i := 0; i < len(h); i += 2 {
  		if h[i] == k {
  			r = i
  			break
  		}
  	}
  	return r
  }
docs: /*
  	Index returns the index of a keader key in Headers.  Return -1 if the
  	key is not present.
  */