add new sample dataset related to mass balance / strain

[dylanbeaudette]

Setting up a new SPC-based example dataset called "bergstrom2018". Shawn Salley is the lead on this.

citation: https://www.sciencedirect.com/science/article/pii/S0016706117314738?via%3Dihub#f0020
background: https://www.sciencedirect.com/science/article/pii/0169555X9090012F?via%3Dihub

bergstrom2018 will be used to develop / test new methods for working with strain calculations and novel vizualizations.

[swsalley]

My mistake, the dataset was actually published in 2019, so it could either go by 'bergstrom2019' or something else with Fraser, FEF, mass balance, strain, etc in the title.

The name 'bergstrom2019' matches other example dataset naming conventions in aqp.

[swsalley]

updated data with horizon elemental concentrations, dropped the 5th landscape position (wetlands soils)
#299
#300

10/2/24, Updated horizon column name capitalization error. https://github.com/ncss-tech/aqp/compare/master...swsalley:aqp:patch-3?expand=1#diff-95e74044cd0ccbf2bdcd09c4abe0963ae42ba1978c60a808522a4f3af614671a

A draft vignette of functions for these data are at
https://github.com/swsalley/bergstrom2019/blob/main/R/massbalance_intro.md

[dylanbeaudette]

Hi Shawn, finally making my way back to this. Can we merge your changes into aqp this week?