Change: added a task struct. With bitfield help has same size of DWORD

Signed-off-by: Giuseppe Monteleone <info@ing-monteleone.com>
New, scheduler no task switch if no task change

Signed-off-by: Giuseppe Monteleone <info@ing-monteleone.com>
Change: added syscall.h. Fixed signals: every task has one signal

Signed-off-by: Giuseppe Monteleone <info@ing-monteleone.com>
Add: variable task size for task

Signed-off-by: Giuseppe Monteleone <info@ing-monteleone.com>
Add: disable Systicks timer when all task are waiting

Signed-off-by: Giuseppe Monteleone <info@ing-monteleone.com>