Test for subcommands specified after parameters.
Re-introduce subcommand parameter.
Leverage defaulting to request_help when subcommand is missing.
Refactor: move subcommand instantiation into Subcommand::Execution.
More refactoring.
Run command_spec and command_group_spec if anything changes.
Pass option values down to subcommand as a Hash.
Pass values of parameters before the subcommand down to subcommand.