Removal of validateUrl - logic for it

[rufuspollock]

@pwalsh why did we remove validateUrl?

I ask as it lead to breakage upstream in data.okfn.org - not the end of the world - but just wondered on motivation :-)

[pwalsh]

It happened in here: #6

We will look at this lib again really soon, and see what we do there.

I should have ensured proper semantic versioning for this API breakage. We also should pin the deps in data.okfn.org

[rufuspollock]

I pinned deps now ;-) - just wondering if it was accidental or intentional to remove it :-)