Order Documentation by learning sequence.

As discussed on the [mailing list](https://groups.google.com/d/msg/phantomjs/7OziTaTiB3Q/yoq988EbmyEJ), the Documentation section has been changed from the default A-Z ordering to something more appropriate to the content.

It appears that the only way this is achievable in Jekyll when using GitHub pages is to use the date stamps in the file names. In this context Jekyll orders by dates first, then A-Z if the dates are equal.