Scene rendering logic is now better

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.

scene so that g_scene can be deprecated later.

in the scene where we can push and pop cameras.

calls so that they take a number of vertices or indexes, not elements.

the Direct3D backend.

Scene and Camera classes.

wrong offset computations.

the Scene code still breaks Direct3D rendering.

issues that were introduced with the Direct3D changes.

cannot used DirectX 10 because my video card only supports DX9, and there
is no compatibility layer. DX11 has feature levels for older hardware so
it would work with a DX9 card, but it's not available for WinXP.

link properly on the Xbox.

with runtime variables is only valid for arrays of texture samples.