SSODA implemented in STUNlib and testclients.

Allows client to get a IPv4 and IPv6 relay address in one allocation.
(https://datatracker.ietf.org/doc/draft-martinsen-tram-ssoda/)
Compile with c99

Do we need to use C90?
Trying to get library more C90 compliant

Did something change on Travis?
Merge branch 'SSODA'