Support tracing multiple pids or a pids of a particular user, set of users or even groups?

[gnewton]

Right now filago only tracks a single pid.
Extend to support:

• multiple pids (would require change in output to indicate pid)
• all pids owned by a user
• all pids owned by a list of users (would require change in output to indicate users)
• all pids owned by the users of a particular group (would require change in output to indicate users)