DistMatrixandSquareMatrixcan optionally store a list of labels corresponding to the underlying elements (e.g. taxa). There are new methods to get values by label. Some APIs changes as a result, for example the file parsers now just return a matrix rather than a(labels, matrix)pair.DistMatrixandSquareMatrixcan be constructed from iterators over pairs of labels associated with distances usingfrom_labelled_distances.