Fix Makefile dependency handling and add install/uninstall targets

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>
Add support for peridic timers and resetting timers

Refactor uev_timer_create() to support a periodic (msec) argument. For
such timers libuev automaticlly respawns them.  Effectively resetting
the timeout using the period value.

Also, refactor argument order to uev_timer_create() and uev_io_create().

Rename UEV_FHIN, UEV_FHOUT to UEV_DIR_INBOUND and UEV_DIR_OUTBOUND.

Remove unnecessary return value for watcher callbacks.  What would those
have been usefu for, ever?  Not even the original code checked the return
value after calling a handler.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>