Additional diversity metrics

[TheOafidian]

• Add support for different alpha diversity metrics and plotting a series of them (add_alphas and tacoplot_alphas)
• Add aitchison distance as a possibility for ordination
• Allow ordering of tacoplot_stack using an optional argument
• Add optional statistical tests to tacoplot_ord (might still be beter ones out there, but now there's a framework to add these)
• Exporting to biom format with to_biom
• Exporting ASV sequences with to_fasta