cosmetics, update file headers (ud-ping.c and svc-pong.h)

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
chore, guard declaration of ud_svc_nego_score() by UD_COMPAT

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
fix, PEBKAC, close secondary (send) socket upon ud_close() and distinguish between PUB, SUB, and PUBSUB sockets

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, rewrite ud-ping tool in terms of new api (not really fully functional yet)

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, hygiene, for ud_msg_s prefer const void* for easier casting

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
Merge branch 'feat/new-api' into next

* feat/new-api:
  minor, hygiene, for ud_msg_s prefer const void* for easier casting
  fix, PEBKAC, close secondary (send) socket upon ud_close() and distinguish between PUB, SUB, and PUBSUB sockets
Merge branch 'tool/ud-ping' into next

* tool/ud-ping:
  minor, rewrite ud-ping tool in terms of new api (not really fully functional yet)
  chore, guard declaration of ud_svc_nego_score() by UD_COMPAT
  cosmetics, update file headers (ud-ping.c and svc-pong.h)
Merge branch 'next'

* next:
  minor, hygiene, for ud_msg_s prefer const void* for easier casting
  minor, rewrite ud-ping tool in terms of new api (not really fully functional yet)
  fix, PEBKAC, close secondary (send) socket upon ud_close() and distinguish between PUB, SUB, and PUBSUB sockets
  chore, guard declaration of ud_svc_nego_score() by UD_COMPAT
  cosmetics, update file headers (ud-ping.c and svc-pong.h)