@param cb a function taking two arguments: an integer severity between
_EVENT_LOG_DEBUG and _EVENT_LOG_ERR, and a string. If cb is NULL,
then the default log is used.
NOTE: The function you provide* must not* call any other libevent
functionality. Doing so can produce undefined behavior.
Redirect Libevent's log messages.
@param cb a function taking two arguments: an integer severity between _EVENT_LOG_DEBUG and _EVENT_LOG_ERR, and a string. If cb is NULL, then the default log is used.
NOTE: The function you provide* must not* call any other libevent functionality. Doing so can produce undefined behavior.