measure and report the time for first and last byte in or out

[ywang19]

in current implementation, it reports response time = timestamp(last byte in) - timestamp(request out) for read, =timestamp(response in) - timestamp(first byte out). but other timestamps like first byte in for read should also be useful, need measure and report out.

[tsg-]

Clarification: this is a new metric (does not replace the existing response time)

[ywang19]

one new time metric "proctime" is added, which maps to the portion of response time excluding data transfer time.