code: func (b *ByteBuf) WriteUInt16(v uint16) (n int, err error) {
  	b.Expansion(2)
  	Uint16ToBytesTo(v, b.buf[b.writerIndex:b.writerIndex+2])
  	b.writerIndex += 2
  	return 2, nil
  }
docs: // WriteUInt16 write uint16 value to buf using big order
  // return write bytes count, error