Use vctrs to establish new classes of data

[njtierney]

I think that the new modern approach is to use vctrs::new_vctr

For example:

naniar/R/shade.R

Line 16 in 885de6f

structure(x,

Could / should probably be replaced with something like what @mitchelloharawild has written here:

https://github.com/mitchelloharawild/distributional/blob/e1fe78652c74a969e0c0d505b12445d5f36af664/R/distribution.R#L17

See also: https://vctrs.r-lib.org/articles/s3-vector.html