Build Modernization, Fix bugs & Packaging

[vejeta]

• Modernization effort on the build system to support modern and legacy Unix systems: Modern: Linux, BSD, MacOS, etc...
• The Administrator user doesn't need to be edited in header.h.dist as it was needed historically. It will be obtained from the current shell user, and the binaries will be installed in $HOME/conquer, while if we install through packages, they will be installed in the standard folders for that distribution.
• Some modernization on the C codebase to support new standards and environments.
• Packaging system to build .deb packages with for Debian/Ubuntu and APK with Melange for Alpine/Wolfi.
• Updates to the documentation system for modern groff.
• CI support for building these packages through GitHub Actions.