Added a new benchmark using a Connection Pool

On a Core2 Quad Q9550 (Six years old) running Debian 7 inside VMware on Windows Server 2008 i got 12k requests/s with rubinius-head

```
$ wrk http://localhost:3000
Running 10s test @ http://localhost:3000
  2 threads and 10 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency   811.95us    4.07ms  38.15ms   98.48%
    Req/Sec    12.04k     2.82k   14.89k    89.94%
  112474 requests in 10.01s, 7.94MB read
  Socket errors: connect 0, read 0, write 0, timeout 28
Requests/sec:  11234.99
Transfer/sec:    811.91KB
```