New Mellite version 2.42.0 and rendering tutorial

A new version of the Mellite computer music environment has been released. It contains many small improvements and fixes, particularly addressing the usability on macOS. I have also authored a new text tutorial, using the Paul Stretch extreme time stretching algorithm as an example for the use of the embedded FScape non-realtime audio rendering language. Mellite now comes with multiple binary downloads that contain the full runtime system, thus simplifying installation for most users.