Create a function that will return string keys for options.
By default, keys will be equal to the value returned by name.
A static string prepended to all keys
If null, keys will not include names of subcommands. If given, this string be used will join subcommand names to the beginning of keys. For options that are in a root command, this has no effect. For option in subcommands, the subcommand name will joined. The root command name is never included.
If true, returned keys will be entirely uppercase.
- characters in option names will be replaced with this character.