Help command can be interchanged out by disabling it, compact formatting for commands

I've seen commands displayed both ways, so I'm not sure which is more "unix-y", but this allows the user to switch between a compact format and the current format for commands. The current format for commands looks like so:

```
$ chat
usage: chat [<flags>] <command> [<flags>] [<args> ...]

A command-line chat application.

Flags:
  --debug              enable debug mode
  --help               Show help.
  --server=127.0.0.1   server address

Commands:
  help <command>
    Show help for a command.

  post [<flags>] <channel>
    Post a message to a channel.

  register <nick> <name>
    Register a new user.
```

By setting the following parameters:

```
app.SetCompactUsage(true)
app.SetHelpCmd(false)
```

The new output from above will look like:

```
$ chat
usage: chat [<flags>] <command> [<flags>] [<args> ...]

A command-line chat application.

Flags:
  --debug              enable debug mode
  --help               Show help.
  --server=127.0.0.1   server address

Commands:
  post        Post a message to a channel.
  register    Register a new user.

```

Again, I've seen the usage done both ways so these little switches allow you to leverage both. You don't have to merge this, but I found it useful for my own project.
Adding the tabs seemingly fixes the help text alignment between flags and commands. This might be doable another way but adding these seems to fix that issue even with short command names vs longer names.