Currently, the tooling just keeps the whatever benchmark order
that was present, and this is fine nowadays, but once the benchmarks
will be optionally run interleaved, that will be rather suboptimal.

So, now that i have introduced family index and per-family instance index,
we can define an order for the benchmarks, and sort them accordingly.

There is a caveat with aggregates, we assume that they are in-order,
and hopefully we won't mess that order up..