Add functions for structured progress logging

internal/output/output.go

@@ -0,0 +1,14 @@
+package output
+
+import (
+	"github.com/apex/log"
+)
+
+// Progress logs a progress type event
+func Progress(key string, perc float64, msg string) {
+	log.WithFields(log.Fields{
+		"type":       "progress",
+		"key":        key,
+		"percentage": perc,
+	}).Info(msg)
+}