Remove unused imports in goto.__init__
Add print_help and print_version functions
Add module to handle exceptions
Add module to communicate with exchange file
Rewrite architecture
Use doublequotes for strings in goto.storage
Explicit label storage API
Move .goto file to .goto/labels
Implement backend to list/add/rm/update aliases
Implement frontend to list/add/rm/update aliases
Add arguments to handle label subcommand
Add .goto/aliases to $PATH