Move duration and size to units pkg

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)

units/duration.go

@@ -0,0 +1,31 @@
+package units
+
+import (
+	"fmt"
+	"time"
+)
+
+// HumanDuration returns a human-readable approximation of a duration
+// (eg. "About a minute", "4 hours ago", etc.)
+func HumanDuration(d time.Duration) string {
+	if seconds := int(d.Seconds()); seconds < 1 {
+		return "Less than a second"
+	} else if seconds < 60 {
+		return fmt.Sprintf("%d seconds", seconds)
+	} else if minutes := int(d.Minutes()); minutes == 1 {
+		return "About a minute"
+	} else if minutes < 60 {
+		return fmt.Sprintf("%d minutes", minutes)
+	} else if hours := int(d.Hours()); hours == 1 {
+		return "About an hour"
+	} else if hours < 48 {
+		return fmt.Sprintf("%d hours", hours)
+	} else if hours < 24*7*2 {
+		return fmt.Sprintf("%d days", hours/24)
+	} else if hours < 24*30*3 {
+		return fmt.Sprintf("%d weeks", hours/24/7)
+	} else if hours < 24*365*2 {
+		return fmt.Sprintf("%d months", hours/24/30)
+	}
+	return fmt.Sprintf("%f years", d.Hours()/24/365)
+}