Consider adding schema.org to RDFa core default profile

Hi,

Adding the schema.org namespace to the default profile would ease the
deployment of schema.org in RDFa 1.1 when using CURIEs, so that authors
don't have to worry about defining the namespace. schema.org might not
compare to the other namespaces in terms of number of documents found in the
wild, but it's bound to grow given the push from the search engines to get
it deployed on the Web. Implementors will most likely hard code this prefix
binding in their implementations anyways, so it might as well be
standardized.

'schema' is a good prefix candidate (we use it in Drupal and I've seen
people using it when writing RDFa snippets). While 's' is another option in
line with the prefix 'v' of data-vocabulary.org, it is more cryptic. so I'd
vote for schema:.

Steph.