Get a list of all :class:`Strategy` subclasses.

def get_strategy_types():
    """Get a list of all :class:`Strategy` subclasses."""
    def get_subtypes(type_):
        subtypes = type_.__subclasses__()
        for subtype in subtypes:
            subtypes.extend(get_subtypes(subtype))
        return subtypes
    return get_subtypes(Strategy)