sixtyforce 2.0

This version requires macOS 10.9 (Mavericks) or later.

What's new in this version of sixtyforce:

* Added a missing dsp instruction.
* Added a warning when running under Rosetta.
* Fixed executable memory mapping failing on Rosetta.
* Fixed a potential race condition in audio rendering.
* Fixed a bunch of small bugs.
* Converted several lingering parts of the app to Swift.