support relative time in timestamp parameter

for our tor exit abuse ticket system (which is sending auto-replies) it would be nice to be able to include a direct exonerator URL with our IP and say a lookup for yesterday (or 2 days ago)

The auto-reply text is static so the URL would also have to be a static string

http://metrics.torproject.org/exonerator.html?ip=1.1.1.1&timestamp=-1&lang=en

Trac:
Username: exonerator