Use libev for inputs and timeouts

Bugs:

* There seems to be a noticeable frame loss when window
  is being opened/closed. But the same problem also exists
  in master/next, so this is not a regression.
* Using --sw-opti and --benchmark at the same time causing
  compton to draw more frequently than permitted by the
  arguments. That is because the sleep interval calculation
  is flawed. Not really a regression either.

Verified still working:

* Usual painting
* Fade
* Benchmark mode
* --sw-opti (with or without benchmark mode)
* DBus
* Unredir delay

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/compton.h

@@ -491,11 +491,6 @@ ensure_glx_context(session_t *ps) {
 }
 #endif
 
-static inline time_ms_t
-timeout_get_newrun(const timeout_t *ptmout) {
-  return ptmout->firstrun + (max_l((ptmout->lastrun + (time_ms_t) (ptmout->interval * TIMEOUT_RUN_TOLERANCE) - ptmout->firstrun) / ptmout->interval, (ptmout->lastrun + (time_ms_t) (ptmout->interval * (1 - TIMEOUT_RUN_TOLERANCE)) - ptmout->firstrun) / ptmout->interval) + 1) * ptmout->interval;
-}
-
 /**
  * Get the Xinerama screen a window is on.
  *