Unity engine v8

Unity engine players downloaded by Trippin on first use (see src/engine.rs).

v8 adds unity_orbit_foundry (13 shows in all), and eased bass/kick/mid reactivity for unity_prism, unity_aurora, unity_pillars and unity_basscore.

Built from master 62d8d36 with Unity 6000.3.25f1 on macOS (the Windows player was cross-built there).

• TrippinEngine-macos-v8.zip: sha256 b91ed377c50d14e5ad2d026ede615683f17df22d08a97480de58669bdd34c25d
• TrippinEngine-windows-x64-v8.zip: sha256 b99b6845cc86b79467efc2fbd10ad271aec9e54e0baa293b6b4f2fb674b5a14f