Updated TODO
Changes and fixes for backface culling

Triangles, quads and rectangles use `back?` and `inside?` instead of
'back and 'front, and reorder vertices instead of setting culled face.
Rendering with an inconsistent view matrix (e.g. scaled negative x)
renders the correct face.
Render with upper-left origin by flipping projection matrix upside-down

This is instead of rendering and then flipping; i.e. make the GPU do
the work in parallel instead of the CPU serially after drawing.
Combined transformations with their inverses