Support through Python 3.12, 62-state support for NEXUS outputs, and support for PHYLIP distance/similarity matrices

This release incorporates contributions from @catsmith to ensure compatibility with Python versions 3.9 through 3.12. (As a result of these changes, Python 3.8 is no longer supported.) To accommodate software like PAUP* and @edmondac's fork of MrBayes (https://github.com/edmondac/MrBayes), the symbol set for NEXUS outputs has been extended to 62 symbols (0-9, a-z, and A-Z). This release also adds support for the use of --table distance and --table similarity options (along with the --proportion and --show-ext flags) with outputs in PHYLIP (.phy and .ph) format to produce PHYLIP-formatted distance or similarity matrices.