Consistent CLI

[InputUsername]

The CLI is currently minimal but already inconsistent.

• rescrobbled without args

  • on first run creates a config file
  • if Last.fm credentials are set, asks for a login

• rescrobbled -v/rescrobbled --version

  • prints the version and exits

• rescrobbled config

  • prints the effective config and exits

Especially if #204 gets implemented, these behaviors should probably be turned into subcommands, with bare rescrobbled only running in daemon mode.