Finish preprocessor. Now it correctly handles $IFDEF, $IFNDEF, $ELSE, $ENDIF and $DEFINE. Still not enterprise level, as has some flaws, but is okay to process hedgewars sources.

foreach(dir "Fonts" "Forts" "Graphics" "Locale" "Maps" "Music" "Sounds" "Themes" "Missions" "Names" "misc" "Scripts")
  add_subdirectory(${dir})
endforeach(dir)