Add 'pry' as development dependency
Remove tmux enabled keys from keys file
Remove --tmux option; use --command instead
Add --command to README
Adjust CLI options banner
Add --help to CLI options
Add 'thor' as runtime dependency
Replace OptionsParser with Thor
Remove unused Github::Auth::Options
Remove usernames param from Cli#keys
Add option for GitHub host and keys path
Update Cli acceptance test to match new syntax
Update README with new command line syntax