Unify all the SDL_*RunApp() functions into just SDL_RunApp()

makes the SDL_main code shorter

Also added a generic SDL_RunApp() implementation for platforms that
don't really need it.

Some platforms (that use SDL_main but haven't been ported yet) are
still missing, but are added in the following commits.

build-scripts/fnsince.pl

@@ -92,7 +92,6 @@ foreach my $release (@releases) {
 #  until a later release, but are available in the older release.
 $funcs{'SDL_WinRTGetFSPathUNICODE'} = '2.0.3';
 $funcs{'SDL_WinRTGetFSPathUTF8'} = '2.0.3';
-$funcs{'SDL_WinRTRunApp'} = '2.0.3';
 
 if (not defined $wikipath) {
     foreach my $release (@releases) {