Previously, Boolean defaults were printed as strings, which lead to true and false being printed as "1" and "", respectively. With this change, they are now printed as "true" and "false".
To keep language consistent, three methods were changed in InputOption:
* `InputOption::acceptParameter()` -> `InputOption::acceptValue()`
* `InputOption::isParameterRequired()` -> InputOption::isValueRequired()`
* `InputOption::isParameterOptional()` -> `InputOption::isValueOptional()`
The InputDefinition::asXml() method was also modified to update the `accept_value` and `is_value_required` attributes.