README update: messaging sample added
examples: messaging client/server
rpc: PUSH interface

+unittests
iocore: set SO_REUSEADDR on server sockets
iocore: close server sockets on shutdown
tests: udp PUSH test; rely on SO_REUSEADDR
rpc: move core RPC module
README update
docs: general messaging scheme
netlink: start to separate Netlink class from IOCore
iocore: bring back non-abstract UNIX sockets
docs: fix the scheme before the IOLoop transition
iocore: shared IOLoop
iocore: remove dead code

Also simplify shared ioloop usage
docs: iproute dia update
iocore: use AddrPool instead of cyclic nonce