Feature Request: Done d/N

[PeterHewat]

This extension is great for estimating the time remaining.
What would be even better is if you could also keep track of the work that has already been done with a d/N for example.

[rdw-software]

I've looked into adding something like this after hacking the extension for my own purposes, but I think this might raise a UI issue: Where should such a progress report be displayed? I can only think of Milestones, but in the Projects view there's not really any space after adding the estimated total time.