Tracking last-known-location of users.

[amcgregor]

Syntax: !seen <user> [@<otheruser>]

Expected result: [<otheruser>: ]<user> was last seen in <channel> on <date>

If user is currently online: [<otheruser>: ]<user> is currently online in <channel-list>

[emberian]

Possible extension: ...on <date> doing <action> where action is parting #chan, saying "<quote>", etc.