Subcommand usage help incorrectly uses singular label when max=0 (unlimited), should use plural

[bryarrow]

When generating usage/help text for subcommands, CLI11 currently uses a logic similar to:

out << get_lable(app->get_require_subcommand_max() < 2 || app->get_require_subcommand_min() > 1
           ? "SUBCOMMAND"
           : "SUBCOMMANDS");

However, according to the code in class App, max=0 means "unlimited", i.e., any number of subcommands are allowed. In this case, the logic above will use the singular label ("SUBCOMMAND"), which is incorrect in English (and also causes issues for i18n).

[phlptp]

The SUBCOMMAND vs SUBCOMMANDS is easy enough to fix here, I am curious about the i18n issues, and what you think would make that easier.