support profile-n

unlike with tick-n, profile-n fire timer interrupt in every cpu.
user can use specific cpu to profile:
	ktap -C cpu -e "profile-10us {}"

Possible usage:
	profile-1s { ... }
	profile-1ms { ... }
	profile-10us { ... }

This patch also introduce kp_state recursion context, for disable
tracing when execute timer closure.

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>
move mainthread stack initization out of kp_newthread

This will make kp_newthread be a little more faster.

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>
add timer example into README

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>