security/vuxml: Document multiple vulnerabilities in irc/irssi

Security: CVE-2018-7054
Security: CVE-2018-7053
Security: CVE-2018-7052
Security: CVE-2018-7051
Security: CVE-2018-7050

PR: 226001
Reported by: tj@mrsk.me (email)
Reported by: David O'Rourke <dor.bsd@xm0.uk>