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- Changed ``Task`` and ``TaskGroup`` ``start`` methods to exit with a return code when a task fails. The ``Command``
task also passes the return code of the process that failed in that particular case.
- Added ability to create and add ``TaskGroup`` instances to an existing task group with just a string to create one,
or a list of strings to add multiple groups with the given names, providing an iterable list of the tasks created.
- Added string conversion to ``_Addressable.base_name`` initialisation to ensure that tasks are created with names that
are strings.