Bugfix: bash/linux does not support setting high bits on return codes

Bugfix: bash/linux does not support setting high bits on return codes

These bits are generally reserved for process-specific behavior.
Explicitly return 0 for success and 1 for failure.
The firewall program already does this.

The return codes from the main functions of each project will continue to utilize all of the bits as designed.
This will allow for projects that link to the library to get the actual return codes while simultaneously being compatible with Linux and Bash.

Later versions may provide alternative ways to get the error code from within the shell.
For example, if a specific return code environment variable is set, then the program could populate that environment variable on exit (clearing it on start).