code: func hexToKeybytes(hex []byte) []byte {
  	if hasTerm(hex) {
  		hex = hex[:len(hex)-1]
  	}
  	if len(hex)&1 != 0 {
  		panic("can't convert hex key of odd length")
  	}
  	key := make([]byte, len(hex)/2)
  	decodeNibbles(hex, key)
  	return key
  }
docs: // hexToKeybytes turns hex nibbles into key bytes.
  // This can only be used for keys of even length.