Reads up to max bytes from source

Property definitions

core $ Reader :: read_bytes
	# Reads up to `max` bytes from source
	fun read_bytes(max: Int): Bytes do
		assert max >= 0
		var cs = new CString(max)
		var rd = read_bytes_to_cstring(cs, max)
		return new Bytes(cs, rd, max)
	end
lib/core/stream.nit:225,2--231,4