Remove unnecessary header inclusion

Delete the statement `# include <stdbool.h>` from 'src/scheduler.c'.

'stdbool.h' defines C's `bool` type. This isn't used anywhere in the
source.
Modify the type of the queue index variables

Shift the type of `iQueueFront`, `iQueueRear`, and `QueueMax` from
`size_t` to `in32_t`.

Normally pointer arithmetic would be performed using `size_t` variables
but for the sake of the wrapping functions making use of `int32_t` will
prevent errors through type promotions and conversions.
Fix issues relating to `enum EElevatorDirection`

Add the missing `;` to the end of the definition of
`enum EElevatorDirection`, and remove the type declaration from
`GetElevatorDirection(void)`.

The use of a type declaration in `GetElevatorDirection(void)` implies an
incomplete type (which cannot be instantiated).
Include the `void` specified to `Peek()`

The declaration of `Peek(void)` previously lacked the `void` specifier
in its declaration in `GetElevatorDirection(void)`.

While not mandatory, the lack of `void` introduces a declaration that is
ill-formed and can generate issues.
Cover for the lack of `inline`

Make use of a blank define to remove instances of the `inline` keyword.

The current compiler has no definition for `inline` (introduced in C99).
Rather than removing every instance of the word make it invisible to the
compiler until there is support.
Introduce missing header file

Add the file 'cmsis_os.h' to the top of 'src/scheduler.c'.

'cmsis_os.h' includes the declarations of the all operating system
constructs that are required to interfaces with it.