Support zipped datapackage file

[danielhuppmann]

When trying to use this package in IAMconsortium/pyam#323, it seemed like I needed to unpack a zipped file first (compared to just reading it as package = Package(path) using datapackage-py).

Was I doing this wrong, or is zip really not supported?

[rgieseke]

Yes, it's currently not supported as i hadn't encountered Data Packages in the wild which i wanted to read ...

Since OPSD is having them for example, it might be a good feature to add though!
Otherwise unpacking first or on the fly would be the way to go ...