flow: fixes false-register sharing.

This is indeed a "fix" but i'd like to have a better solution, sharing
register values across basic-blocks. TBD.
cleanup
examples: adds an TCP echo server example using zero-copy networking.
some documentation
doc: project number update
flow: some doc updates + dead code cleanup
http: first bits on request/connnection buffer rework
http: HttpConnection debug trace support
http: HttpConnection::ref()/unref() gets a label debug helper
belongs to the last commit (wrt my .cpp)
base: Socket::read(Pipe*, size_t) actually got a fix
base: adds Socket::read(Buffer&, size_t) to not read more than that bytes
rename HttpMessage{Processor,Parser}
belongs to last commit
http: rename HttpMessageParser::{process,parseFragment}
http: rename Vary to HttpVary
http: rename/move enum VaryMatch into HttpVary::Match
http: rename HttpConnection::watch{Input,Output} to want{Read,Write}
http: moved HttpRequest::write(Source*) into .cpp file
http: HttpConnection code cleanup and a minor fix wrt. 413