* Defined the single-column single-position (SCSP) situation where a
single column of the input is blit on a single position of the VRAM.
Provided optimized assembly and a specialized bopti_render_scsp()
function.
* Improved the rendered by reducing the amount of computation and
clarifying the semantics of the rbox.
* Separated rbox setup from clipping by making bopti_render_clip() a
purely abstract superset of bopti_render_noclip().
