Support Dev Containers add GitHub Codespaces.

Co-authored-by: Rodolphe Lepigre <lepigre@mpi-sws.org>

self extracting archives can now have several index files

minor bug fixes

minor improvments

 - better handling of savefiles
 - a couple of new, minor options
 - a couple of minor bug fixes

several small bug fixes

remove locations in .po files

support for zsh

do not clear screen on startup when given option -q

only run test_bin.sh in start.sh, not in profile.sh

making most scripts POSIX compliant

as well as some bugfixes and minor improvment