Mention MIME type parameter 'content'

[tomdonaldson]

(Also see original mention on the IVOA Applications mail list.)

Section 8 on MIME types currently mentions the serialization parameter and the generic charset parameter. The DataLink specification recommends using the content parameter (application/x-votable+xml;content=datalink) to denote VOTables that are DataLink responses.

According to RFC2046 and RFC2048, introducing new ad-hoc parameters along these lines is not forbidden. Unless the content parameter is already being used in other VOTable contexts, it might make sense to mention it in VOTable section 8 to bring it in sync with the DataLink recommendations, and avoid other standards reinventing the same thing with a different name.