• feat: add OpenSUSE 15.2 to the officially supported distros
• enh: install-ttyrec.sh: replaces build-and-install-ttyrec.sh, no longer builds in-place but prefers .deb and .rpm packages & falls back to precompiled static binaries otherwise
• enh: packages-check.sh: add qrencode-libs for RHEL/CentOS
• enh: provide a separated Dockerfile for the sandbox, squashing useless layers
• doc: a lot of fixes here and there
• chore: remove spurious config files
• chore: a few GitHub actions workflow fixes