Macrons to be added to special characters

We're based in New Zealand and the Māori language uses macrons over letters to denote a longer vowel sound. At the moment in the list of special characters the closest thing I can find is the tilda (wiggly line above a letter) but that's not technically correct and it should be a macron. I would like to suggest that special vowels with macrons be added to the special characters list. In Te Reo Māori (the Māori language) a macron can change the meaning of a word. For example from the film industry - the famous wētā workshop should be spelt with macrons over the e and the a, and is the name of an insect. Without the macrons weta means excrement. Quite the different meaning from two little lines!