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.
* removed the __call() method in Container: it means that now, there is only
one way to get a service: via the get() method;
* removed the $shared variable in the dumped Container classes (we now use
the $services variable from the parent class directly -- this is where we
have a performance improvement);
* optimized the PHP Dumper output.
