ESS-DIVE V2

This release is associated with V2 of https://doi.org/10.15485/1960313.

Changes:

• scripts for soil and sediment visual metrics, soil cations, and soil extractable iron
  soil_cec.R
  soil_iron.R
  soilsediment_visual_metrics.R
• edits to sample catalog and l2 scripts
  sample_catalog_matrix.R
  l0_to_l2.R