+'GetRelativeTimestamp': Pre-emptively override the relative timestamp generated
+by MWTimestamp::getRelativeTimestamp(). Return false in this hook to use the custom
+output.
+&$output: string for the output timestamp
+&$diff: DateInterval representing the difference between the timestamps
+$timestamp: MWTimestamp object of the current (user-adjusted) timestamp
+$relativeTo: MWTimestamp object of the relative (user-adjusted) timestamp
+$user: User whose preferences are being used to make timestamp
+$lang: Language that will be used to render the timestamp
+