README: Fixed getconf command in build instructions (#72)

getconf NPROCESSORS_CONF isn't a valid command. The correct command is getconf _NPROCESSORS_CONF.

core: support conversions from 10-bit formats

Fixes #16

Authored-by: niki-on-github <arch@local>

core: avoid leaving garbage buffers on exit

clang-format, no-zoom and render-inactive