We still need to include <lol/format> because of platforms that do not have full
C++20 support such as the N******* S*****.

A lot more removals are coming. I’m thinking merging the Application and
ApplicationDisplay classes, as well as removing the corresponding -Data
classes.

Executables that use libbullet are now 1 MiB smaller (stripped!).

We now just look for SDL2/SDL.h (the regular location) and SDL.h (when
the user provides their own location for this header).

Sometimes libEGL.so can be available (provided as a symlink
by Debian diversion packages) while EGL/egl.h isn’t.

The only reason we had to keep this was for emscripten builds. We can
now use SDL v2 using “emconfigure ./configure CFLAGS="-s USE_SDL=2” and
a few additional flags.

SDL_Mixer v2 is not available in emscripten packages but either it will
be added at some time, or I will get rid of it altogether. An alternate
solution could be this code snippet I found:

    cd SDL2_mixer
    emconfigure ./configure --prefix=$(pwd)/dist --enable-music-ogg --disable-music-ogg-shared CFLAGS="-s USE_VORBIS=1"
    emmake make install