Add default values to --help output

[TooTallNate]

Fixes #38.

I also fixed a bug with Boolean types showing undefined in the output.

Before:

    -b, --b undefined  a boolean type
    -l, --l <list>     a list type
    -n, --n <n>        a number type
    -o, --o            no default value
    -s, --s [value]    a string type

Now:

    -b, --b          a boolean type (defaults to true)
    -l, --l <list>   a list type (defaults to [1,2,3])
    -n, --n <n>      a number type (defaults to 42)
    -o, --o          no default value
    -s, --s [value]  a string type (defaults to "milk")

Thought: for bool types we could say "on" or "enabled" (and "off" or "disabled")
instead of true/false to make the output a little bit more human-friendly.

[leo]

Thanks! Exactly, I'd say "Disabled by default" and "enabled by default". But only if the user passed a default bool value.

[leo]

@TooTallNate You removed the default value for -v. Have you checked if running <cmd> -v and <cmd> --version still returns the version of the app?

[TooTallNate]

Yes, -v / --version still work as expected because of

args/src/index.js

Lines 339 to 344 in f838e16

	// And immediately output it if used in command line
	if (this.raw.v || this.raw.version) {
	console.log(version)
	process.exit()
	}
	}

.

Removing the default value just removed it from the help output ("defaults to v1.0.0" doesn't make much sense).

[leo]

@TooTallNate Great, thanks! ❤️ I have also added you as a collaborator.