Changes in version 2022-05-10 (2022-05-10)               

  - add vis_index() to return a logical vector of the points to keep

  - Fix off-by-one error in C code
  - Tidy priority queue implementation
  - Handle duplicates in vis_simplify()
  - Duplicate points are given negative effective areas in
    vis_effective_areas()

               Changes in version 2022-05-08 (2022-05-08)               

  - Initial release