Updates for iOS13

[n8henrie]

I'm new to iOS development, so no hard feelings if this doesn't fix things the "right way."

But with these changes I'm able to build and run on iOS13.

Fixes #1

NB: I use homebrew (not MacPorts), so I had to change the ao import path. It seems like homebrew is by far the more popular MacOS package manager these days; I think using it instead of MacPorts might help encourage contributions. Additionally, it doesn't require installing libao with elevated permissions.

[pulsely]

Have to agree switching to Homebrew makes a lot of sense.

• Will test and merge your changes when the new Homebrew coming out along with Catalina, expecting by the end of the month
• Also, will have better writeup on setting homebrew with libao