Cleaner display of errors

[divarvel]

Right now the error display is a bit crude:

./subcommands.js number add AA BB int: invalid int: AA int: invalid int: BB

Usage: testCli number add INT INT
add two integers

Arguments:
INT                 int value
INT                 int value

Options:
[--help, -?]        Display help about this program
[--version, -V]     Display the version of this program