Make next release 4.0.0

[zabidenhtf]

Because I and many other contributors made big changes for Li-Ri. And I'm think will better make next release 4.0.0 instand 3.1.7

[petitlapin]

I'm fine with it. About the scope, it needs for me to have at least:

• SDL 3 (if it works fine on all the platforms of course)
• the new audio
• the SDL_ttf PR
• the translation working with SDL_ttf
• remove all the global variables (at least most of them can be removed easily)

If there are other things, that's better, but once we have these, I think we can do a new one