library for implementing command-line interfaces

 cli is a library for implementing powerful command-line interfaces in
 Go. cli is the library that powers the CLI for Packer, Serf, and Consul.
 .
 Features:
  - Easy sub-command based CLIs: cli foo, cli bar, etc.
  - Optional support for default subcommands so cli does something other
    than error.
  - Automatic help generation for listing subcommands
  - Automatic help flag recognition of -h, --help, etc.
  - Automatic version flag recognition of -v, --version.
  - Helpers for interacting with the terminal, such as outputting information,
    asking for input, etc. These are optional, you can always interact with
    the terminal however you choose.
  - Use of Go interfaces/types makes augmenting various parts of the library a
    piece of cake.