Godot remake

Remade the game in Godot.

Not much has changed, but:

• It’s now playable in the browser, but the performance is really poor.
• It’s also playable on Android now, either through the browser or the APK file.
• Instead of getting a speed penalty when jumping or moving up, sliding up a ramp will now temporarily slow you down, better matching the original “Speed is key” limitation.