Adds a mac implementation for next_keyboard_layout() function, now the get_voice_name() function, on macOS will also return its language code

[GruiaChiscop]

the get_voice_name() function must return the voice name with its language code because, on macOS, all eloquence voices have the same name for each voices. This is done to be easier to distinguish between these voices.

[samtupy]

Hi,

Thanks for both this contribution and the speak_to_file method in the tts_voice class!

Though it's not an issue, it seems that both of the pull requests you opened somehow ended up on the same branch,so actually the changes in #116 are also contained in #117 E. the pr with speak_to_file also contains this next_keyboard_layout function.

This isn't a problem in the end, but if it seems confusing that one pr will likely get closed and the other merged, this is why. Nevertheless both changes will be included. My plan after verifying that everything is OK is to close this pr (#116), and instead merge #117 which contains both the tts_voice additions as well as next_keyboard_layout.

It's usually best to create a new branch for every pull request, as this avoids things like this popping up.

Thanks again, we'll have these merged soon!

[GruiaChiscop]

Oops, yes, I noticed that after I opened the pr, but I had no time to fix that. Anyway, I can close this pr and let only #117 open. But what I forgot to mention in the description of #117 is that the speak_to_memory() function on macOS can only save files in .wav format, .ogg and opus formats are not supported at all by AVAudio, probably in the future I'll figure out how to use Bass to write the file, but for now, I think it's just fine.