* implement `yQuads()` and `draw_octant()`, pretty obvious extensions of
existing code. to allocate up to 3 potential remainder lines, consider
that octants will often appear in a rectangular subset of the terminal.
we want the distributed excess uniformly distributed across such a
region. so:
* one excess row: break symmetry in any direction (pick an arbitrary
tetrad and use it everywhere)
* two excess rows: go to alternating tetrads
* three excess rows: break symmetry, do not use three contiguous tetrads
* our `Octant`s are octary arrays of `bool`, provided as a somewhat
opaque constant table
* the 8-line copy-and-paste draw based on the `Octant` is not the
prettiest thing in the known universe
* we could generalize `draw_sextant()` and `draw_octant()` like
notcurses did, almost certainly
* oh bird thou never wert
with that said, i don't think `draw_octant()` is actually being called
lol, so let's not merge this yet. happy to hear early feedback, though.