logging-v2: basic stream operator
logging-v2: support old logging api
time_now_str() prints usec
logging-v2: refactor logging code into do_log() and do_vlog()
switch #pragma once to include guard
logging-v2: temporarily disable custom streaming
logging-v2: more friendly api, just use: INFO << msg
logging-v2: add when() conditional logging
logging-v2: replace when() with the smart trick in google-glog
logging-v2: rewrite logging
add Log_debug
logging-v2: have to add LOG_ prefix to prevent conflicting with other names
logging-v2: code cleanup