Most .h files were not used to declare the externally visible variables
and functions of the .cpp files, but only to #include things and declare
things that were needed by that .cpp file itself. This resulted in a lot
of duplication.
Now the .h files only declare what is externally visible from the
corresponding .cpp files. Starfighter.h includes all the other .h files,
and all .cpp files only #include "Starfighter.h". Functions and
variables that were not used outside the .cpp file that contained them
were marked static. Variables defined in .h files were moved to the
appropriate .cpp files.