Specify MIME type for Thing Description

[benfrancis]

It's necessary to specify a MIME type for a Thing Description to denote that it is not just JSON but is a Web Thing Description with an implied default context.

I suggest using application/td+json as per the latest W3C proposal on the assumption that we will converge on that format.

[benfrancis]

Question: Should the MIME type for the REST API payloads be the same or different to the MIME type of the Thing Description?

I wonder if they may be two separate data types.