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.