This allows us to separate accidentally unused, from explicitly unused
parameters, which allows us to turn on such checks in the compiler.

The generally recommended way is to include it from source files, not
headers. We had a mix of both. Let's try to be consistent and follow the
recommended way.

They have very different purpose, so make things easier to work
with by having multiple directories.

Bit shifting gives an approximate, but not properly accurate value
when upconverting. Do a proper calculation.

Either by casting, or switching to a more appropriate type
for the variable.