feat(sointu-track): accept filename as command line parameter

Closes #122.

CHANGELOG.md

@@ -5,6 +5,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 ## Unreleased
 ### Added
+- Passing a file name on command line immediately tries loading that file (#122)
 - Massive rewrite of the GUI, in particular allowing better copying, pasting and
   scrolling of table-based data (order list and note data).
 - Dbgain unit, which allows defining the gain in decibels (-40 dB to +40dB)

cmd/sointu-track/main.go

@@ -55,6 +55,13 @@ func main() {
 		recoveryFile = filepath.Join(configDir, "Sointu", "sointu-track-recovery")
 	}
 	model, player := tracker.NewModelPlayer(cmd.MainSynther, recoveryFile)
+	if a := flag.Args(); len(a) > 0 {
+		f, err := os.Open(a[0])
+		if err == nil {
+			model.ReadSong(f)
+		}
+		f.Close()
+	}
 	tracker := gioui.NewTracker(model)
 	output := audioContext.Output()
 	defer output.Close()