Added a flag to subtree_by_leaf_names and to remove_single_children to allow the root to keep a single child; the default is still to collapse the root.
Added a flag to subtree_by_leaf_names and to remove_single_children to allow the root to keep a single child; the default is still to collapse the root.

mdrasmus/compbio,wutron/compbio,mdrasmus/compbio,wutron/compbio