Read the content of a map, len keys and values

Property definitions

msgpack :: read $ Reader :: read_msgpack_map_data
	# Read the content of a map, `len` keys and values
	private fun read_msgpack_map_data(len: Int): Map[nullable Serializable, nullable Serializable]
	do
		var map = new Map[nullable Serializable, nullable Serializable]
		for i in [0..len.to_i[ do map[read_msgpack] = read_msgpack
		return map
	end
lib/msgpack/read.nit:157,2--163,4