func NewDecoder(enc *Encoding, r io.Reader) io.Reader {
	return &decoder{enc: enc, r: r,
		buf:       bytes.NewBuffer(nil),
		leftovers: bytes.NewBuffer(nil)}
}
func NewDecoder(enc *Encoding, r io.Reader) io.Reader {
	return &decoder{enc: enc, r: r,
		buf:       bytes.NewBuffer(nil),
		leftovers: bytes.NewBuffer(nil)}
}
// Returns a new decoder. Data will be read from r, and decoded
// according to enc.