transmute_obs: Replace columns in [taxmap()] objects
Description
Replace columns of tables in `obj$data` in [taxmap()] objects. See
[dplyr::transmute()] for the inspiration for this function and more
information. Calling the function using the `obj$transmute_obs(...)` style
edits "obj" in place, unlike most R functions. However, calling the function
using the `transmute_obs(obj, ...)` imitates R's traditional copy-on-modify
semantics, so "obj" would not be changed; instead a changed version would be
returned, like most R functions.
Dataset name, index, or a logical vector that indicates which dataset in
`obj$data` to use.
...
One or more named columns to add. Newly created columns can be
referenced in the same function call. Any variable name that appears in
[all_names()] can be used as if it was a vector on its own.