Basic reporter

[at15]

Related #12 #14

• total request body size (might exceed int64?, use uint64?)
• total response body size
• http response code count
• error percentage (in current tests, err is not tirggered yet, though it should be)
  • how golang http client handle non 2xx response code, treat it as error?
• distribution of response time
  • hey store every thing in ram, which is low effficient https://github.com/rakyll/hey/blob/master/requester/print.go#L190
  • we can use pre allocated bucket and fill them in, then aggregate them based on slow and fastest
  • or use this histogram library https://github.com/VividCortex/gohistogram

[at15]

Close in favor of #60

Now we will store even more than just min, max, histo, raw full metrics and even traces will be stored, this does not have the performance of target database as long as the workload generator in different nodes, though if trace is enabled on server side, the penalty without sampling could be large ...