Draft: Several updates: Functional shell w/o TTY, replace RustCrypto, update dependencies/Rust

Most significant changes:

• Update dependencies
• Update Rust Edition
  • Replace deprecated features
• Refactor to satisfy Clippy lints
• Replace outdated RustCrypto with alternatives as outlined in the updated README
• Implement functional std(in|out|err) without TTY
• The schema of the used key file has changed since it contained redundancy

But:

• TTY/PTY remains dysfunctional
• The event loop implemented in this MR is to be replaced:
  • It configures non-blocking I/O
  • No async-Rust has been introduced and no polling is used
  • Temporary fix: introduce delay to avoid stressing the CPU

Also, I have taken the audacity to list myself as a contributor, I hope this is ok.