Avoiding to copy the response body to /dev/null

o runtime can reusage sockets even though if the body
is not explicitly closed. Forwarding the body contents to a socket was
causing much garbage and ending up with high CPU consumption.

http.Client was shared among workers, instead initing a new client
for each worker.
Import rakyll/pb, so pb doesn't break boom builds.
Minor fix for latency percentiles.
Merge pull request #18 from mdakin/minifix

Minor fix for latency percentiles.
Added a CSV output option
Change output command format
Disable status bar
Merge pull request #19 from pasc/csv_output

Added a CSV output option
Tweaking the description of output flag, updating the usage on the README.
Merge upstream.