AudioUnit version

[giulioz]

Not really a mergeable PR but some work in progress to have the emulator hosted inside DAWs such as Logic Pro
Example: https://www.youtube.com/watch?v=DxIF8f454ns

Challenges and changes:

• Global and static variable can't work, as it needs support for multiple instances
• The UI with SDL cannot work, so basic framebuffer LCD support is needed
• The multi-threaded audio renderer can't work, as it needs to be driven by the host

PS: Thank you for this amazing project!