Asynchronous event notification library (extra)

 Libevent is an asynchronous event notification library that provides a
 mechanism to execute a callback function when a specific event occurs
 on a file descriptor or after a timeout has been reached.
 .
 It is meant to replace the asynchronous event loop found in
 event driven network servers. Currently, libevent supports /dev/poll,
 kqueue(2), event ports, select(2), poll(2) and epoll(4).
 .
 The libevent_extra library includes code for HTTP, DNS, RPC, and so
 on.
 .
 If you're writing software that uses libevent's protocol support, you
 need to link libevent_core and libevent_extra as well.