-Move task_init() and task_activate() prototypes from include/sched.h to include/nuttx/sched.h. These are internal OS functions and should not be exposed to the user.
-Remove references to task_init() and task_activate() from the User Manual.
-Rename task_init() to nxtask_init() since since it is an OS internal function
-Rename task_activate() to nxtask_activate since it is an OS internal function