Fix HTTP benchmark examples.

 - The server crashed with concurrent workload due to the match-tree based router rebuilding in multiple threads at the same time (all the code isn't really thread safe!)
 - Removed the hard-coded limit of 5k requests from the requester
 - Using a request concurrency level of 100 by default
 - Fixed an issue with incrementing a 64-bit token (is not an int)
Implement a small DNS cache to speed up multiple resoles of the same host name.