Whip the ol' llama's ass (fix ncvisual rotation)
* notcurses: flush cursor change requests #673
* rotator: verify ncplane_rgba and ncblit_rgba
* ncblit: rename, accept ncblitter_e #674
* rotator: render from rgba
* rotator: get to rotation
* rotator: add a pi/4 turn at the end
* normal: reuse incoming plane for rendering #672
* rotator poc: rotate a fullplane gradient #672
* normal demo: place visual correctly
* rotator: verify ncplane_rgba and ncblit_rgba
* ncblit: rename, accept ncblitter_e #674
* rotator: render from rgba
* rotator: add a pi/4 turn at the end
* normal: reuse incoming plane for rendering #672
* rotator poc: rotate a fullplane gradient #672
* normal demo: place visual correctly
* rotator poc: throw some red into gradient
* rotator poc: done #662
* oiio: ncvisual_resize() needs set ibuf pointer #662
* normal: only need erase at top of loop
* visual poc: shorter delay
* normal demo: center rendered visual
* comment ncvisual_resize() call
* ncvisual_rotate: call ncvisual_details_seed()
* ffmpeg ncvisual: fix rotation #662
Replace the singly-linked z-axis with a doubly-linked list,
and reimplement all z-axis moves as O(1) functions.
Eliminate ncplane_move_{above/below}_unsafe(), as there are no
longer unsafe moves.
Unify ffmpeg/oiio/null implementations, where possible. This effectively
required placing all three in the same file, which meant they're all now
C++. Update FFmpeg implemenation to be C++-usable. Implement
ncvisual_rotate_cw() and ncvisual_rotate_ccw() #515. Move most of tetris
over to Visual from Plane #558. Add bgra_to_rgba(), necessary for
creating ncvisual from BGRA memory. Implement ncvisual_from_rgba()
and ncvisual_from_bgra() #557. Add unit tests on ncvisual rotation.
