Add retrieving recent events to the REST interface

Based on an internal discussion, we need to add an extra convenience features to the REST interface.

We'd like to retrieve the recent "n" events: the implementation of this is not difficult. We calculate the startID based on how many events we want. Right now this cannot be done reliably because right after we determined the startID, new events can arrive, so the last "n" is no longer the last "n".