Override package guidelines with own set of guidelines (static only)

pass in three-column data frame to `calc_limits` with `site`, `parameter_code`, `guideline`, which would override limits from the package for those specific sites/params

Start at the calc_limits entry point and inspect how package guidelines are selected. Add support for a static three-column data frame containing site, parameter_code, and guideline, then verify that supplied rows override limits only for the matching sites and parameters.

Written by the indexing model from the issue text.