One of the joys of working with ScummVM was that, using existing
Common functionality, the entirety of the original's CompressedFile
class could be reduced to a couple of lines. As such, CompressedFile
doesn't really need it's own seperate files anymore.
This is necessary for at least message sending, and probably other
areas, that needs to be able to pass class filtering for message
targets. And I could figure out a clean way to use the built-in RTTI