This patch adds support for at/cron-like jobs that need an absolute
timer. The API supports waking up with an UEV_HUP callback event if the
wall clock changed due to NTP or user input while waiting.
- uev_cron_init()
- uev_cron_set()
- uev_cron_start()
- uev_cron_stop()
A very simple cronrun example/test program is also included.
Signed-off-by: Joachim Nilsson <troglobit@gmail.com>