Support lambdas in module commands
Enable UBSan in travis
Merge branch 'lambda'
Give clients a "default" identifier

This makes things play nice eg. if there's ever going to be
a dedicated config section for clients. As an example, the
detached status could be stored per client:

    <Network freenode>
        <Chan #znc>
            Key = secret
            Buffer = 1000
        </Chan>

        <Client default>
            <Chan #znc>
                Detached = true
            </Chan>
        </Client>
    </Network>
ListClients: add identifier column