This moves all the byte swapping utilities into a header named Swap.h.
A dedicated header is much more preferable here due to the size of the
code itself. In general usage throughout the codebase, CommonFuncs.h was
generally only included for these functions anyway. These being in their
own header avoids dumping the lesser used utilities into scope. As well
as providing a localized area for more utilities related to byte
swapping in the future (should they be needed). This also makes it nicer
to identify which files depend on the byte swapping utilities in
particular.
Since this is a completely new header, moving the code uncovered a few
indirect includes, as well as making some other inclusions unnecessary.
At first there weren't many enums in Volume.h, but the number has been
growing, and I'm planning to add one more for regions. To not make
Volume.h too large, and to avoid needing to include Volume.h in code
that doesn't use volume objects, I'm moving the enums to a new file.
I'm also turning them into enum classes while I'm at it.
