libev is modelled after libevent (http://monkey.org/~provos/libevent/), but aims
to be faster and more correct, and also more featureful. Examples:

- multiple watchers can wait for the same event without deregistering others.
  (registering two read events on fd 10 and unregistering one will not
  break the other)

- fork() is supported and can be handled
  (there is no way to recover from a fork when libevent is active)

- timers are handled as a priority queue
  (libevent uses a less efficient red-black tree)

- supports absolute (wallclock-based) timers in addition to relative ones,
  i.e. can schedule timers to occur after n seconds, or at a specific time.

- timers can be repeating (both absolute and relative ones)

- detects time jumps and adjusts timers
  (works for both forward and backward time jumps and also for absolute timers)

- can correctly remove timers while executing callbacks
  (libevent doesn't handle this reliably and can crash)

- less calls to epoll_ctl
  (stopping and starting an io watcher between two loop iterations will now
  result in spuriois epoll_ctl calls)

- usually less calls to gettimeofday and clock_gettime
  (libevent calls it on every timer event change, libev twice per iteration)

- watchers use less memory
  (libevent on amd64: 152 bytes, libev: <= 56 bytes)

- library uses less memory
  (libevent allocates large data structures wether used or not, libev
  scales all its data structures dynamically)

- no hardcoded arbitrary limits
  (libevent contains an off-by-one bug and sometimes hardcodes a limit of
  32000 fds)

- libev separates timer, signal and io watchers from each other
  (libevent combines them, but with libev you can combine them yourself
  by reusing the same callback and still save memory)

- simpler design, backends are potentially much simpler
  (in libevent, backends have to deal with watchers, thus the problems)
  (epoll backend in libevent: 366 lines, libev: 89 lines, and more features)

whats missing?

- evdns, evhttp, bufferevent are missing, libev is only an even library at
  the moment.

- no priority support at the moment.

- kqueue, poll (libev currently implements epoll and select).