Not all programs support this feature for now, but that’s because they
don’t support the scene framework either, and will need patching. Also
the default postprocess is deliberately exaggerated for now.

Now TickDraw() can be called several times per frame, because we
may have several scenes. This is expected, but it will require
some adjustments later.

Add String.split(char) to split into an array, and add a simple
char const * + lol::String free operator.

There might be issues with lolremez but at first sight it seems to work.

This doesn’t work properly yet because PICO-8 uses a few language
extensions; we will have to decide whether to modify the Lua
interpreter, or change the code on the fly, or something entirely
different.

For now, all it can do is read and decompress .p8.png files.

Various changes in GCC, clang, and libflex had triggered build failures.

If SDL_CFLAGS is defined to a non-empty value, even spaces, a later
test will wrongly succeed and think SDL_CFLAGS is a user override.