Added threading header
Added threading implementation for uCOS-III
Updated README with threading example.
Rename os_thread_sleep_ms()
Updated package file.
Improved comments.
Improve code readability.
Initialize system timer when running os.
Forgot to include header.
Merge branch 'master' into ucos-iii-threading-impl

Conflicts:
	package.yml
Added a function to sleep a guaranteed duration.
Updated header file.
Changed thread sleep unit to microseconds.
Merge pull request #38 from nuft/ucos-iii-threading-impl

Threading api with uCOS-III implementation