REL: Version 2.2 updates

[carlwilson]

• modularised the specification into multiple files;
• added specification.yaml file for site/PDF structure and generation;
• added forwarding for unversioned latest profile link;
• moved old specification\metadata.md file to metadata.yaml;
• updated v2.2 profile with version changes;
• updated spec-publisher project to get the latest pub changes;
• ./doc directory contains parts necessary for the spec site and PDF generation;
• new create_site.sh and create_pdf.sh scripts;
• fixed Markdown lint issues;
• removed old site generation artefacts;
• added CC-BY LICENSE file; and
• cleaned .gitignore.