console: figure out parent/child spans should be displayed

[davidbarsky]

While #9 is more focused on the data collection side of things, this issue is concerned with how parent/child relationships should be rendered in the console. Possible approaches:

• @hawkw suggests that something like htop's tree mode would be useful.
• being able to dynamically highlight an individual task and view its tree would be also helpful, as @tobz suggested.

[hawkw]

Some inspiration:

• htop tree mode:
  
• pstree(1):
  
• tracing-tree:
  
• reqray:
  
• Jaeger tree + timeline view:
  

I think a tree-mode would probably end up being a different view mode from the top(1)-style task list view we have currently. It would also be nice to have a way to highlight one task in the list view and see just its parent context, which we could add to the current view pretty easily, I think. Might be good to start with that before writing a tree-mode?

[carllerche]

A timeline view would definitely be awesome, but maybe for the MVP we start by showing the "current state" as a backtrace type view and go from there?

[hawkw]

A timeline view would definitely be awesome, but maybe for the MVP we start by showing the "current state" as a backtrace type view and go from there?

yup, that's what i'm thinking as well. now that #13 gave us the ability to highlight individual tasks in the top tasks view, we have a nice way to select a task and expand it to show the full context.

tree and timeline views would be really nice to have in a future iteration!