add a totalReadItems() method to GoogleReader class

Hi,

I've added this method because I've written a GR importer, and I needed the total to display a progress.
Sorry it's not perfect (the URL is quite hard-coded, language-related replace(…) etc).

We are quite in a hurry to import GR data, I've got other things to focus on.

BTW, thanks for your very useful lib!!

best regards,