timer skeleton
add linux-kernel-style list_for_each macro
timer development

Add use of timer_create() and timer_settime(), changed classical
do_handle_event() function definition, assuming that only one kind of
event is possible.
add test program for timer widget

Not compiling.
reduce spinbox's use of redundant headers
timer widget builds

As itimerspec needs -std=gnu99 or -D_POSIX_C_SOURCE=199309L, I put the
details related to system timer into source of the widget, and hide them
with an incomplete type timer_internal_data_t.

Sample program timer.c can be used to test the effect of CPU usage
saving when using "pseudo-realtime".
add sample program text_clock using timer widget