This is silly. I can see that someone decided to restrict targeting
to one ship as a difficulty setting, but that's not a very good way
to achieve different levels of difficulty.
Also added more music and slowed down RE.ogg.
The source code contains routines to initialise all these resources, but also
functions to load from and store to external files. Support for external files
has now been removed; this removes a potential difference between compiling
with or without USEPAK, and makes it easier to change missions in the code.