Suggestion: Some form of hook to add extra data before closing segment

I think it would be awesome if we could have some sort of hook before the segment is closed to add more information, for example add annotations about processing times etc.

I'm using restify and the server codebase is big so being able to hook into the segment before it's sent would save making drastic changes to the codebase to allow for the situation.

For example I want to include some simple stats like memory/cpu usage as part of the trace. People would probably find it useful to add other things here as well.

Currently I'm looking to fork the repo just so I can add this in to help troubleshoot production issues.