Implement command line parsing

[jcouball]

Implement the command line parsing in chezroot to satisfy these requirements:

The purpose of chezroot is to call chezmoi via sudo when appropriate, passing its command line arguments directly to chezmoi (with some exceptions). Calling via sudo or non-sudo is based on the command given by the user on the command line.

• chezroot will need to be able to determine the "command line items" given by the user: global flags, command, subcommand, and command specific options and flags, etc.

• For most commands, chezroot will call chezmoi with all the arguments it received in a spawned subprocess. stdout, stderr, and the process status returned from chezmoi should be returned by chezroot

• chezroot will need to add some global options to the chezmoi command line. For instance, --destination DIRECTORY and --source DIRECTORY.

• Certain command line items will be disallowed by chezroot. In this case, chezroot will display an error instead of calling chezmoi. For instance, the --destination, --source, and --config global options are not allowed. And the --apply and --watch options to the edit command are not allowed.

• Certain global flags that chezroot will need to filter out for itself and not pass to chezmoi. For instance, the global flag --profile=NAME will be removed from the command line passed on to chezmoi. chezroot will need to use the given NAME.

• chezroot will need to intercept some commands to wrap their functionality (do something before and/or after the chezmoi command is called) or do something totally different without calling chezmoi at all

• chezroot will add certain commands that it will implement and not pass on to chezmoi. An example of this is the profile management command as described in this repository's README.md