Added taxonomy_distance() for calculating pairwise taxonomic
distances between OTUs from a taxonomy table.
Added support for filtering taxonomy assignments by confidence scores
through a new confidence argument in taxonomy_tree() and
taxonomy_distance().
Extended vs_cluster_unoise() and vs_cluster_size() with new arguments for
controlling output from clustering output: clusters and uc. The uc
argument was also added to vs_usearch_global().
Added a verbose argument to functions that print progress messages or other information to the console.
Updated vs_optimize_truncee_rate() and vs_optimize_truncqual() with an
option to randomly sample 10,000 sequences when the input contains more than
10,000 sequences, thereby reducing computation time.