Add modified Mahalanobis filters

[nfrerebeau]

References:

• Beier, T., Mommsen, H. (1994). Modified Mahalanobis filters for grouping pottery by chemical composition. Archaeometry, 36(2):287-306. DOI: https://doi.org/10.1111/j.1475-4754.1994.tb00971.x.
• Mommsen, H. (2012). The importance of a reliable grouping - neutron activation analysis (NAA) data of Mycenaean pottery sherds re-evaluated with the Bonn filter method. Journal of Archaeological Science, 39:704-707. DOI: https://doi.org/10.1016/j.jas.2011.11.002.
• Mommsen, H., Kreuser, A., Weber, J. (1988). A method for grouping pottery by chemical composition. Archaeometry, 30(1):47-57. DOI: https://doi.org/10.1111/j.1475-4754.1988.tb00434.x.
• Riehle K, Kistler E, Öhlinger B, Heitz C, Ben-Shlomo D, Jung R, Mommsen H, Sterba JH, Gimatzidis S, Fantalkin A, Prillwitz S, Hein A, Geissler L, Lehmann G, Kindberg Jacobsen J, Posamentir R, Schlotzhauer U. (2023). Neutron activation analysis in Mediterranean Archaeology: current applications and future perspectives. Archaeological and Anthropological Science, 15(3):25. DOI: https://doi.org/10.1007/s12520-023-01728-1.
• Sterba, J. H., Mommsen, H., Steinhauser, G., Bichler, M. (2009). The influence of different tempers on the composition of pottery. Journal of Archaeological Science, 36:1582-1589. DOI: https://doi.org/10.1016/j.jas.2009.03.022