Implement Boore et al. (2020)

See: https://pubs.geoscienceworld.org/ssa/srl/article/91/2A/977/580478/Revision-of-Boore-2018-Ground-Motion-Predictions

This model is an update to the Boore et al. seed models considered in NGA-East. It includes a site term and we should seek guidance on implementation specifics from the GM group.

Preliminary work includes verifying the existence of hard rock tables for easy inclusion in the seed logic tree