Apple Silicon Native App

[alexclst]

Now that Apple Silicon Macs are in the wild, there should be a version of MacDown that runs natively on them. From experience, I know the app works under Rosetta, but we know that is only a temporary solution. Someday years from now Rosetta will probably be gone. So, MacDown should become a Universal app sooner rather than later.

[alexclst]

Just realized this duplicates #1215, so I'm closing this.