[install] Add --sys to urt-config

Signed-off-by: Shahbaz Youssefi <ShabbyX@gmail.com>
[doc] add build, install and license docs

Signed-off-by: Shahbaz Youssefi <ShabbyX@gmail.com>
[doc] typo fix

Signed-off-by: Shahbaz Youssefi <ShabbyX@gmail.com>
[update] simpler check on user vs. kernel space

Signed-off-by: Shahbaz Youssefi <ShabbyX@gmail.com>
[bugfix] [linux] next_period and wait_period clash

They were both updating the next period time, while together they should
have only done so once per period.

Signed-off-by: Shahbaz Youssefi <ShabbyX@gmail.com>