Tests are not actually ran on appveyor for now, since they all fault for
some reason. For now, we just build them. Also, some tests are disabled
on msvc entirely, because they don't even compile. We'll need to look
into those, later. They are disabled using `MSVC_DONT_BUILD`.
- Any non-externally-visible declarations should be `static`.
- Casting away the `const` qualifier from pointers-to-const is
dangerous. All but one instance of this are now correct. The one
instance where we can't keep `const` is one where toxav code actually
writes to a chunk of memory marked as `const`. This code also assumes
4 byte alignment of data packets. I don't know whether that is a valid
assumption, but it's likely unportable, and *not* obviously correct.
- Replaced empty parameter lists with `(void)` to avoid passing
parameters to it. Empty parameter lists are old style declarations for
unknown number and type of arguments.
- Commented out (as `#if DHT_HARDENING` block) the hardening code that
was never executed.
- Minor style fix: don't use `default` in enum-switches unless the number
of enumerators in the default case is very large. In this case, it was
2, so we want to list them both explicitly to be warned about missing
one if we add one in the future.
- Removed the only two function declarations from nTox.h and put them
into nTox.c. They are not used outside and nTox is not a library.
