RtNotifications.java:44-45: Implement markAsRead(), thread(final...

The puzzle `913-3f99f964` in [`src/main/java/com/jcabi/github/RtNotifications.java`](https://github.com/jcabi/jcabi-github/blob/master/src/main/java/com/jcabi/github/RtNotifications.java) (lines 44-45) has to be resolved: Implement markAsRead(), thread(final int number) operations in RtNotifications. Don't forget about unit tests.

The puzzle was created by Dmitri Pisarenko on 22-Jan-15.

Estimate: 30 minutes, role: IMP.

If you have any technical questions, don't ask me, submit new tickets instead. The task will be "done" when the problem is fixed and the text of the puzzle is removed from the source code. Here is more about [PDD](http://www.yegor256.com/2009/03/04/pdd.html).