Implement robust alternative to SES

[Vladimir Mikryukov]

• Implement Knijnenburg et al. 2009 approach (as a robust alternative to SES) in phylogenetic diversity estimation.

See:

• Botta-Dukát Z. 2018: https://akademiai.com/doi/abs/10.1556/168.2018.19.1.8
• Knijnenburg et al. 2009: https://doi.org/10.1093/bioinformatics/btp211