Unfortunately, there seems to be a difference in how the `hello_world` example processes rate and volume changes. I'm not sure if it doesn't adjust rate for samples while speaking. In any case, arguably there are just going to be differences in platforms that I can't account for, so this may just have to be. Hopefully it doesn't interfere with actual usage.
* Fix broken delegate method signature.
* Add `NSRunLoop` into `hello_world` example so delegates are called. Presumably, MacOS apps already run one of these, but the example didn't.
* Add necessary dependencies, build script, and `NSSpeechSynthesizer` backend.
* Get very basic speech working.
Needs a delegate to handle queued speech, and currently segfaults if one is set.