security/vuxml: Document multiple vulnerabilities in irc/irssi

Security: CVE-2017-15721
Security: CVE-2017-15722
Security: CVE-2017-15723
Security: CVE-2017-15727
Security: CVE-2017-15228

PR: 223169
Reported by: David O'Rourke <dor.bsd@xm0.uk>