VSEARCH 2.23.0

Update documentation. Add citation file. Modernize and improve code. Fix several minor bugs. Fix compilation with GCC 13. Print stats after fastq_mergepairs to log file instead of stderr. Handle sizein option correctly with dbmatched option for usearch_global. Allow maxseqlength option for makeudb_usearch. Fix memory allocation problem with chimera detection. Add lengthout and xlength options. Increase precision for eeout option. Add warning about sintax algorithm, random seed and multiple threads. Refactor chimera detection code. Add undocumented experimental long_chimeras_denovo command. Fix segfault with clustering. Add more references.