Write value over two signed bytes, following 1 metadata byte

Property definitions

msgpack :: write $ Writer :: write_msgpack_int16
	# Write `value` over two signed bytes, following 1 metadata byte
	fun write_msgpack_int16(value: Int)
	do
		write_byte 0xD1
		write_bytes value.to_bytes(n_bytes=2)
	end
lib/msgpack/write.nit:112,2--117,4