Consider an absent `:prog` for command help

Start with the cli/dispatch path that formats help output when no :prog option is supplied, using the reproduction in the issue. Check the generated Usage and Run lines, then add regression coverage for the absent-program case. Done means both lines omit the unwanted extra space while the existing command help remains unchanged.

Scenario

Sometimes a program does not have a clear usage name.

For example, a program might be invoked via clojure -M:cli <some-command> [some-options].

In these cases, I don't specify :prog as a dispatch option.
bb cli lets me do this, but it results in an (admittedly nitpicky) output formatting issue.

Repro

For example:

(require '[babashka.cli :as cli])

(cli/dispatch {:cmd {"foo" {:fn identity
                            :doc "foo command help"}}}
              ["--help"]
              {:help true})

Outputs:

Usage:  [options] <command>

Commands:
  foo  foo command help

Options:
  -h, --help  Show this help

Run " <command> --help" for more information on a command.

It's a minor quibble, but notice the extra space before [options] in Usage: [options].
And after Run " on the last line.

Proposal

If :prog is not specified, don't display an extra space character in formatted outputs.

Next

Happy to do up a PR if this seems interesting to you.