Parent command flags are duplicated in subcommands

[mdippery]

A change related to #42 allowed subcommands to inherit flags from their parent. Unfortunately, this change has resulted in some duplication of flags. As shown in the example above, the flags -h, -v, and -t are now printed twice in the help output when help for subcommands are shown, which is unexpected and looks a bit odd. It's especially pronounced in subcommands in which the parent command does not have any flags; two blocks for -h, -v, and -t are printed consecutively now, like this:

Options:
            --date FORMAT  Show dates in "absolute" or "relative" format
            --grep STRING  Show only comments matching STRING
  -n LIMIT, --limit LIMIT  Only show n comments
            --oneline      Output log in a more compact form
            --raw          Print raw comment bodies
        -h, --help         Show this message
        -v, --version      Print the name and version
        -t, --trace        Show the full backtrace when an error occurs
        -h, --help         Show this message
        -v, --version      Print the name and version
        -t, --trace        Show the full backtrace when an error occurs

[mdippery]

Closing this since I opened a pull request in #44.