iocore: cumulative commit, custom services

* custom services register
* service discovery
* proper addr usage
* fix envelope stream parsing

FIXME: deprecates parse_envelope?
iocore: remove deprecated code (parse_envelope)
tests: update to the current state
examples: push client/server
gitignore update

ignore clonedigger output
iocore: introduce ports

Ports are addresses of services on a node. As with TCP/UDP
ports, each service can be addressed with host:port pair.

One can get port number of a service with IOCore,discover()
call.
iocore: use flags in envmsg header
examples: update
iocore: NLT_DGRAM flag fix

+ examples update