Added test client in Siege directory

Hey @devcritter do you mind just having a look at the test script I did in Siege. @rcrichton im not sure if you also maybe want to have a quick look and indicate anything im missing or doing wrong
It would be great if we could set the concurrent and reps params when loading the script, rather than hardcoding them. I think the quickest way to do this is just pass the script params through to siege (since we're already listing the siege params in the readme):
```
siege $@ --log=siege_log.csv --file=siege_url.txt
```
(the `$@` is the array of command params)