BuildStatusPrinter: also print overall progress / percentage done

Would be nice if the status printer printed an overall progress percentage in addition to the (42/N) [recipe -> fetch] based on how much has been done already.

We now schedule lots of build steps and recipes in parallel, but it's very confusing to get any idea of where we're at in terms of progress on systems with higher CPU count.

My naive idea was that we have two bits of data:

1. number of recipes completely done
2. N build steps/stages per recipe
3. number of recipes partially done (if available)

So we could come up with a 'done' percentage based on 1 and 2, with 3 for extra granularity.

Does that sound feasible? Is that data available in the BuildStatusPrinter?