Use w3.org TD Context

[vcharpenay]

As mentioned in PR #180, the official namespace URI can be now used for the default context, as follows:

{
  "@context": "http://www.w3.org/ns/td",
  "@type": "Thing"
}

This URI is much more compact than the current Github URI and I would be in favor of including this change in the coming WD. It requires, however, that the context under w3.org remains up-to-date.

[sebastiankb]

Thanks! This namespace is now used everywhere in the TD spec.

[danielpeintner]

It used to be an https url, now it is http again.

Question: Is this change (besides the actual url) intended?