v0.8.1

Added

• A value method is generated when deriving CommandOption for command option choices.
• CreateCommand::NAME associated constant to get the name of the command.
• CommandInputData::parse_field method to directly parse a field without command model.
• CommandInputData::focused method to get the name of the focused field.
• Implementation of CommandModel for Vec<CommandDataOption> and CommandOption for CommandOptionValue.

Changed

• CommandModel and CreateCommand can be derived on unit structs.
• Improved validation of command names.

Fixed

• ParseError::EmptyOption is only returned when parsing subcommands.
  This fixes command models without options or with only optional options.