Refactor sync-ssh-keys.sh and users.conf for improved structure and f… (#12)

* Refactor sync-ssh-keys.sh and users.conf for improved structure and functionality. Enhance error handling, add self-update feature, and streamline user key processing.

* Bump script version to 0.1.0 for release

* Refactor sync-ssh-keys.sh to improve variable declarations and enhance code readability. Update trap command syntax and clarify user key processing loop.

Author: locus313