Begin a new span
        :param name: name of the span
        :param span_type: type of the span
        :param context: a context dict
        :param leaf: True if this is a leaf span
        :param tags: a flat string/string dict of tags
        :return: the Span object

def begin_span(self, name, span_type, context=None, leaf=False, tags=None):
        """
        Begin a new span
        :param name: name of the span
        :param span_type: type of the span
        :param context: a context dict
        :param leaf: True if this is a leaf span
        :param tags: a flat string/string dict of tags
        :return: the Span object
        """
        return self._begin_span(name, span_type, context=context, leaf=leaf, tags=tags, parent_span_id=None)