Revert "Don't use modules"

This reverts commit bffe99aead.

internal/tai64n/tai64n_test.go

@@ -0,0 +1,21 @@
+package tai64n
+
+import (
+	"testing"
+	"time"
+)
+
+/* Testing the essential property of the timestamp
+ * as used by WireGuard.
+ */
+func TestMonotonic(t *testing.T) {
+	old := Now()
+	for i := 0; i < 10000; i++ {
+		time.Sleep(time.Nanosecond)
+		next := Now()
+		if !next.After(old) {
+			t.Error("TAI64N, not monotonically increasing on nano-second scale")
+		}
+		old = next
+	}
+}