New headers and parameters from RFC 3455 and UUI drafts

These changes derive from mail by John Gregg (see http://list.resiprocate.org/archive/resiprocate-devel/msg08665.html). I added additional header to exchange User-to-User information via SIP.
Linux gperf man page suggests that "-k" and "--key-positions" are equivalent.  In the travis-CI build, it didn't run gperf at all (probably because the files are present in the repository) so I will have to test manually to confirm and to ensure travis-CI tests such changes in future.