[dxwg] Pull Request: Change of structure discussed in Oct 24 discussion in Lyon

aisaac has just submitted a new pull request for https://github.com/w3c/dxwg:

== Change of structure discussed in Oct 24 discussion in Lyon ==
The changes here have the following motivations:

- splitting the long list of requirements/recommendations (MUST/SHOULD/MAY) from https://github.com/w3c/dxwg/issues/435#issue-366191828 and https://github.com/w3c/dxwg/issues/242#issuecomment-408916364 into various sections where they can be better contextualised and explained (as consistent bits) to readers

- acknowledging that these recommendations did not fit well as intro material and giving more space in the introduction so that the discussion on types and examples of profiles (https://github.com/w3c/dxwg/issues/435#issuecomment-426928897) can 'breathe' better.

- provide finer-grained introduction (and better alignment) to other relevant DXWG work (the Profiles Ontology and Profile Negotiation)

- put a placeholder for a conceptual model to which the rest can be naturally attached,  and for which the Profiles Ontology would provide a straight implementation as a vocabulary.

- exploit the notion of role as first introduced in the Profiles Ontology as an interesting pattern to represent the functions that (expressions/components of) profiles can play, as sketched in #435.

See https://github.com/w3c/dxwg/pull/489