IO layer: Java API and docs, make Write accept NoAck aux data

Java API and docs for IO, at first only for TCP. Also allow NoAck to take a token which can be used to store a value with the Write which will not trigger an ACK but can be used in case of NACK.

- [x] add UdpFF, including NoAck()
- [x] add UdpConn, including NoAck()