2ping 4.5.1

• 2ping.bash_completion: Make more resilient to failure / missing
  features.
• 2ping.spec: Add missing BuildRequires: systemd.
• Minimum Python version changed from 3.5 to 3.6.
• Minor no-op code and distribution updates.

2ping 4.5

• Added PyCryptodome support (recommended over PyCrypto, though the latter is still detected/supported).
• Replaced best_poller module with Python native selectors module.
• Changed --flood output: dots/backspaces are no longer printed, and loss results / errors display full details.
• --audible tones will only occur if stdout is a TTY.
• Improved hostname/IP display edge cases.
• Added an AF_UNIX --loopback test mode.
• Listener sockets are added and removed as needed, instead of being re-created on each rescan.
• Listener sockets are automatically rescanned periodically.
• Multiple systemd sockets are now allowed.
• A run can be both a listener and a client at the same time (mainly useful for smoke testing).
• Other socket handling refactoring.
• Other code refactoring.
• Listener statistics are displayer per-bind.
• Many, many testing/CI improvements.