add new feature and fix url check error

[ysykzheng]

Hello, I fix url check error.
is.url('http://localhost/') // should be true, but false

and add query parameter ‘url’ for loading data.

[CLAassistant]

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[ysykzheng]

url sample like this:

index.html?url=https%3a%2f%2fraw.githubusercontent.com%2fvincentarelbundock%2fRdatasets%2fmaster%2fcsv%2fDAAG%2fLottario.csv