potentiomap condition classes

Important warnings and errors raised by potentiomap have stable S3 classes so calling code can respond without matching the complete message text. All package warnings inherit from potentiomap_warning; all package errors inherit from potentiomap_error.

Details

Specific classes include potentiomap_input_error, potentiomap_metadata_error, potentiomap_crs_error, potentiomap_arrow_endpoint_warning, potentiomap_uk_instability_warning, potentiomap_kriging_convergence_warning, potentiomap_tps_gcv_boundary_warning, potentiomap_contour_level_warning, potentiomap_contour_support_warning, potentiomap_contour_support_error, potentiomap_contour_threshold_error, potentiomap_contour_uncertainty_error, potentiomap_support_warning, and potentiomap_export_error.