Add statements in Architecture Overview and also DV_EHR_URI description also LINK description to indicate that EHR URIs are 'plain text' and need to be RFC3986-encoded when applied to REST APIs or other URI-consuming contexts.
Add text in the following places to indicate that so-called plain-text URIs are allowed, but have to be RFC-3986-encoded for use in machine-processing contexts:
- text for DV_URI class in UML.
- text in explanatory section in URI section of RM Data types
- explanatory text in section 11 (Paths) of Architecture Overview
Small fixes to text clarity, formatting also added in these sections.