code: function $header(byte) {
      if (start === 0) start = position;
      type = byte >> 4 & 0x07;
      length = byte & 0x0f;
      if (byte & 0x80) {
        offset = 4;
        return $header2;
      }
      return afterHeader();
    }
docs: n-byte type and length (3-bit type, (n-1)*7+4-bit length) CTTTSSSS C is continue bit, TTT is type, S+ is length