pst-vowel – Enable arrows showing diphthongs on vowel charts

The pack­age ex­tends the vowel pack­age (dis­tributed as part of the tipa bun­dle) by al­low­ing the user to draw ar­rows be­tween vow­els to show re­la­tion­ships such as diph­thong mem­ber­ship.
The pack­age de­pends on use of pstricks.