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.
* ncplane_at_* and ncplane_at_cursor_*
We had notcurses_at_yx() expanding into three distinct parts of
the cell structure, and ncplane_at_yx() / ncplane_at_cursor()
writing directly to a cell. It was annoying to remember which
was which. The latter two now have a signature matching
notcurses_at_yx(), while the old functionality has been moved
to ncplane_at_yx_cell() and ncplane_at_cursor_yx(). #476
Fill-type functions used to return 0 for success, and -1
on failure. They now return the number of cells written
on success, similarly to ncvisual_render(). Resolves#427.
Certain unit tests required UTF8 encoding on the output
terminal to work (#428). This includes anything which does
any kind of fill. Add enforce_utf8() checks to all such
tests that were missing them. Unit tests once again pass in
a pure ASCII environment.
Introduce limited plane rotation capability. We currently support clockwise and counterclockwise rotation of planes. Square and rectangular geometries are both supported, but there must be an even number of columns. The atomic unit of rotation is a 2x1 "square" (this assumes .5 cell aspect ratio). We can only rotate those glyphs which have rotated equivalents, and not even all of those. We currently handle only:
* null glyph
* space
* upper half block
* lower half block
* full block
I've added unit tests as well. This functionality is used by our Tetris example in the book
