tries to address issue #29

The existing statistical reporting is a little misleading, particularly the "50%" and "90%" values. The title "50% response times: 123.45 [ms] (mean)" suggests that 50% of all of the responses across all of the bees is 123.45 ms. This is not what is calculated, but that is what would be useful to know.

This series of change sets attempts to address this issue by using `ab -e`, which reports a csv file of the full percentile results. We then aggregate this in the correct way so we can finally specify the overall median ("50%") and 90th percentile values, which are really useful to know.

This change set also includes the `-e/--csv` option for `attack`, to allow the user to see the full percentile statistics across all bees and each of the reporting bees. This is useful for detecting if one of the bees, for example, has a crappy connection.

Sorry there are so many change sets in here. I tried to break each one into manageable chunks that logically corresponded with the changes that were made. If there's anything else I can do to clarify this, please let me know.