pkg/timestamp: create timestamp package

pkg/timestamp/timestamp.go

@@ -0,0 +1,13 @@
+package timestamp
+
+import "time"
+
+// FromTime returns a new millisecond timestamp from a time.
+func FromTime(t time.Time) int64 {
+	return t.Unix()*1000 + int64(t.Nanosecond())/int64(time.Millisecond)
+}
+
+// Time returns a new time.Time object from a millisecond timestamp.
+func Time(ts int64) time.Time {
+	return time.Unix(ts/1000, (ts%1000)*int64(time.Millisecond))
+}