v2.4.8—remember this day

OK, after a few kinda rough releases--it's been a difficult month--I feel really, really good about this one. I believe 2.4.8 will honor its righteous progression of powers-of-two. Very few new features here, but instead lots of subtle fixes and analysis. Also, full Unicode 14.0 support on macOS now!

• Multithread the [view] and [yield] demos (#1613)
  • improves their performance on most platforms
  • provides examples for multithreaded employment of multiple ncpiles
• Fix bug in notcurses-demo where [zoo] left its background plane up
• Fix bug in Kitty graphics rendering where glyphs under opaque sprixcells weren't invalidated, but needed to be
  • Fixes several longstanding bugs in notcurses-demo (#1932, #2297)
• Fix a bad memory leak in ncvisual_stream() (#2286) and several others on error paths (#2282)
• Fix bad memory write when wiping/rebuilding sixel which is partially offscreen (#2287)
• Fix use-after-free in automaton construction that likely never hit anyone, but was lurking (#2279)
• Address scan-build warnings, some of them real, others (i think/hope) not (#1348)
• Allocate auxiliary vectors appropriate for graphics protocol, saving 50% of memory for fbcon / kitty-static
• Don't discount a character simply because wcwidth() returns -1; gets most Unicode 13 working on macOS (#2285)
• Support environment variable NOTCURSES_LOGLEVEL (#2277)
• [keller] demo now exits out when it fails to blit something it thinks ought have worked (#2278)
  • Fix bitmap sizing bug this surfaced
• Add USE_ASAN to build with AddressSanitizer, add several compiler optimization flags for floating point (but not the rollup -ffast-math, which includes -ffinite-math-only, which is incompatible with libav, which sometimes reports NaN for timing information). Do not enable this unless actively debugging; it will greatly reduce performance!

The man he stepped up to the microphone and he gave it a kiss.
It was a big wet, slippery kiss.
He had sweat dripping off of his nose onto the windscreen.
As he looked out over the audience he said,
"God bless you, God bless you one and all."
Then he took a can of Ronson lighter fluid
and he squirted it over the top of his head,
and proceeded to light himself on fire,
and as he stood there glowing he said,
"Remember this day."