Various code cleanup changes

1. fix up the `@file` tags, and update a couple of comments.

2. missed a few SCREEN conversions.

3. declare s_foo global variables and some functions static.

4. give functions with no arguments prototypes. i.e.

        bar foo() { ... } -> bar foo(void) { ... }
        extern bar foo(); -> extern bar foo(void);

I'm not sure what your reason is behind the lack of "void" in these functions.  The lack of void turns them into old style function definitions, allowing you to call the functions with arbitrary arguments without compiler warning you (e.g. Timer_InterruptRun).  It doesn't cause a problem with the current code, but it isn't really the behaviour what you want either.