Dillsocks: Protocol library for libdill

Principles:

1. The goal is to allow for true micro-protocol that can be composed like lego blocks to form full-fledged protocols.
2. Currently we have big protocols (hundreds of pages, e.g. 3GPP) and small protocols (tens of pages, e.g. IETF). We want microprotocols (specification one paragraph long).
3. To achieve that we need vertical composability (e.g. TCP on top of IP; HTTP on top of TCP)...
4. And horizontal composability (e.g. HTTP switches to WebSockets; STARTTLS)
5. Protocol initiation and termination is not abstracted; must be done in protocol-specific way.
6. Sending data and receiving data is abstracted. Two abstractions are used: bytestream and messages.
7. Sending and receiving must not presuppose each other.
8. Sending and receiving with metadata (as with sndmsg, recvmsg) is not abstracted and must be done in protocol specific way.
9. The system must be able to support purely "structural" protocols, for example one that joins two uni-directional protocols into a single bi-directional one.

Some protocols have to be supplied out of the box, to give people something to play with in the beginning. Options include:

1. TCP bytestream
2. UNIX domain bytestream
3. UDP
4. Simple framing (size + data)
5. Line protocol (CRLF-terminated lines of text)
6. HTTP
7. WebSockets
8. SMTP
9. Version and/or capability negotiation protocol
10. SSL
11. TCPMUX
12. WebSocketMUX
13. PGM
14. DCCP

Structural protocols:

1. Redirecting to/from file.
2. Combining two unidirectional protocols into one bi-directional
3. Splitting bi-directional protocol into two uni-directional
4. Throttler (both for bytestreams and messages)