Improvments to the scheduler

[DrDeano]

Currently, the initial scheduler is round robin and preempts the current running task when the RTC fires a interrupt. We would like to improve this by:

• [ ] Adding time slices to tasks, e.g. will preempt after 10ms instead of whatever the interrupt is set to.
• [ ] Add the ability for a task to preempt itself, e.g. via a syscall.
• [ ] Maybe add priorities to tasks
• [ ] Only run the idle task when there are no tasks to run
• [ ] Add task termination
• [ ] Add more queues for:
  • [ ] Ready queue
  • [ ] Waiting: I/O / Sleep