Fix problem where malloc and realloc were undefined. Not sure this is a good fix but I'm allergic to autoconf

Rerun aclocal and autoconf

Update URL for nixos package definition.

v1.10.4

Fix CVE-2021-45340 - NULL pointer dereference.

Update stb_image.h from upstream to version 2.30

Make pixel writing with STB work.

Fix double free in src/encoder.c when parsing bgcolor

Fix CI

fix non-unix builds

docs: update link to the Arch Linux package

[AUTHORS] close off my involvement (see https://github.com/libsixel/libsixel/discussions/57)

aminal is now Darktile

list julia wrapper Sixel.jl

HAVE_LIBPNG -> HAVE_PNG