Improved precision of printed results

[rotemdan]

I improved the printed results to account for fractional second and millisecond timing. The rates are still displayed as integers (though now calculated with floating point accuracy) but the elapsed time is now a float with 2 decimal places. Example:

gobench -c 10 -r 1000 -u http://localhost/

Dispatching 10 clients
Waiting for results...

Requests:                            10000 hits
Successful requests:                 10000 hits
Network failed:                          0 hits
Bad requests failed (!2xx):              0 hits
Successful requests rate:             6166 hits/sec
Read throughput:                   5821455 bytes/sec
Write throughput:                   703014 bytes/sec
Test time:                            1.62 sec

[rotemdan]

OK, I found a similar PR but it seems to have since been reverted in the master branch. The only difference between mine and that one is that it changed the number formatting alignment to 13 and had the rates as fractions. I left the length at 10 and kept the rates to display as integers (I don't really think there's a need for fractions since the rates are usually at least in the hundreds or more).