Complete rewrite, added support for hex IDs and auth keys

If you want you can merge the branches. I have added support for hexadecimal IDs and now the URL used to download the tiles is the same as the one in the KML, so now we can download tiles with auth keys. For example this gigapan: http://www.gigapan.com/gigapans/0d54f8d3323a60308eb2ff9831edfe4a has an hex ID and an auth key
I rewrote the code because I wanted to learn better python, so if you want you can leave this branch as a fork