High-level caf-net primitive for custom text protocols

[Neverlord]

From a recent chat discussion: caf.net currently has no high-level primitives to implement custom text protocols like telnet, that split incoming characters into individual messages (in the case of telnet simply by splitting at the newline character).

Ideally, we'd provide an interface in caf.net where users can construct a protocol with a parser of some sort that receives incoming bytes and emits "messages" to a flow. In the case of telnet, that would be trivial: buffer inputs until finding a newline and then emit the line as one message.