Minor updates

• Added new extrapolation.object argument to compare_covariates and map_extrapolation, which allows required inputs to be retrieved directly from the list object returned by compute_extrapolation rather than being manually specified for each function. This was done to streamline function use, minimise redundancy, and increase alignment with the package workflow described in Bouchet et al. (2020). DOI: 10.1111/2041-210X.13469.
• Implemented function ellipsis (...) in compare_covariates so that users who wish to use the function without running compute_extrapolation first can do so.
• Added option to suppress warnings and messages via the verbose argument.
• Update package vignettes to reflect the above changes.