Implement interface for adding other archs

Signed-off-by: Vladislav Levenetz <octal.s@gmail.com>
Add licensing

Signed-off-by: Vladislav Levenetz <octal.s@gmail.com>
Add more comments

Signed-off-by: Vladislav Levenetz <octal.s@gmail.com>
Change arch api interface layout

Signed-off-by: Vladislav Levenetz <octal.s@gmail.com>
Rename threads_api to arch_api

Signed-off-by: Vladislav Levenetz <octal.s@gmail.com>
Add README

Signed-off-by: Vladislav Levenetz <octal.s@gmail.com>