add notice-log for every request

we need a **NOTICE** log for every request, fields::

    type, key, mlen, request_time (like access_log for nginx) 

so we can stat req/s, average srv time, key frequency with awk/grep

here is the format:

      [Wed May 28 15:06:12 2014] nc_request.c:59 req 3 done on c 11 req_time: 0.353 type: SET narg: 3 mlen: 35 key0: kkk-3, done: 1, error:0

maybe add:

- backend addr
- time cost on every phase(parse/forward/coalesce)
- log timestamp should ms/us.  [Wed May 28 15:06:12.xxx 2014]