Reference OGC ModSpec

[nicholascar]

This issue was created in the Profiles Ontology document and is listed in it. Once consensus on addressing it is reached here in comments below, the results will be added to the document and the issue closed.

Refer to OGC Modular Specification policy [[modspec]] and related work in ISO TC/211 [[cfg-mgmt]].

These specifications define how dependencies between 'standards' can be handled in a manageable way.