This simple PR renames the DatagramTransportExecutor (recently introduced via #101) to UdpTransportExecutor. This is done to be in line with the DNS RFC terminology (https://tools.ietf.org/html/rfc1035#section-4.2), because it is less misleading (this class can only really support UDP) and also because for future TCP/IP transport the name "streaming" makes even less sense and they should be named TcpTransportExecutor (#19) and TlsTransportExecutor (#80) respectively. I'm not marking this as BC break because this will be renamed as part of the same release, so outside consumers of this package should not be affected.