The containers no longer force the user to use the ptrdiff_t type for
size information. For convenience, size() now always returns an int,
and the size_s() method offers a way to handle arrays with more than
2 billion elements. Internally, we still use ptrdiff_t, though.

Since so much code had to be changed, I took the opportunity to get
rid of capitalised accessors for classes that are lowercase.

Box objects (AABB) now have the long awaited extent() and center()
methods. Corners are now called “aa” and “bb” for convenience. The
WorldEntity class uses a box3 for its AABB instead of two vec3s.
This allows us to simplify a lot of verbose code.

This sort of pImpl inheritance code code was weird, I got rid of it
and added a new pointer in the TileSet class instead.

Added Texture (by image) update in TextureImage (and tileset)
Added lolimgui first integration pass

scene so that g_scene can be deprecated later.

objects themselves.

and the codec logic.

Added palette in Scene.

return an already created object if necessary.

Tileset : added GetTileSize().

internal format is then automatically deduced. Only a few 8-bit RGB
or RGBA formats are supported for now.

the Direct3D backend.

the Scene code still breaks Direct3D rendering.