Datasets improvements

[Victory]

fixes for v3 of api for datasets using CBOE/VXEEM as an example where we expect the api to call

https://www.quandl.com/api/v3/datasets/CBOE/VXEEM.json?auth_token=########

[Victory]

Sorry these pull requests got a bit messed up. The gist of both of them is that in v3 we were not making the correct call to the api via

        quandl.configure({
            api_version: 3,
            auth_token: "#####"
        });

        quandl.dataset(
            {source: 'CBOE/VXEEM', format: 'json'},
            function(){});