Enhance help text generation

[S4G4R]

Printing help text is currently facilitated using functions such as format-opts and format-table, which might suffice for simple applications. But it quickly gets complicated when we have layers of nested commands and subcommands which have their own opts and args.

Given a spec and args, we should be able to generate help text using a single function call.

Additionally, we could consider including --help or -h as implicit opts for every command and subcommand. Running a command with missing opts and/or args could result in automatically printing help text. cli-matic handles this well.