spanner v1.0.0 and associated MLS sample data

Source code (R and C++) for the spanner package functions get_raster_eigen_treelocs and segment_graph used to segment individual trees from terrestrial and mobile laser scanning  (MLS) datasets, incorporating eigenvalue decomposition and relative point density metrics to locate tree boles and link point returns to individual tree locations using a graph-theory shortest-path approach. Also, included are twelve (12) MLS (GeoSlam ZEB Horizon) scans of ponderosa pine conditions (n = 3 each) with varying treatment histories (e.g., CO: control; TO: thin only; BO: burn only; TB: thin and burn) collected near Flagstaff AZ (lat. 35.234352, lon. -111.750767) in the summer of 2021.