Basic Pagination

Great work on developing a wrapper for the youtube API. I noticed that there wasn't any form of pagination so if a large result was return it couldn't be traversed. I've added some basic changes to allow for this and included a simple example on how to paginate through results.

I haven't done a full on test but I think it should do the job for now :)

Thanks,
I know it's a bit late, but `$resObj->nextPageToken` doesn't exist on the last page, so it leads to a nice warning.