Add data from O'Brien et al. 2001

[joeroe]

Dataset of Palaeoindian points from the Southeastern United States. It's unclear whether the original data is included in the paper in full. They also cite a larger database of Palaeoindian points maintained by David Anderson, but the URL they include (http://www.anthro.fsu.edu/special/paleo/paleoind.html) is unfortunately dead.

• O’Brien, M.J., Darwent, J., Lyman, R.L., 2001. Cladistics Is Useful for Reconstructing Archaeological Phylogenies: Palaeoindian Points from the Southeastern United States. J. Archaeol. Sci. 28, 1115–1136. https://doi.org/10.1006/jasc.2001.0681