Less C89, most const, static funcs

[WillAyd]

Will have to do this in a few passes for other files, but generally we:

1. Are removing C89 style variable declarations at the top of functions
2. Adding const qualifiers where we can
3. Making more functions static that aren't intended to be linked outside of their translation unit

Point 1 helps with code readability, Point 2 can help with code safety and compiler optimization. Point 3 helps with code structure and makes functions "local" to their translaction unit instead of "global"

[mroeschke]

Thanks @WillAyd