MAINT: Various 2.2 tasks

[carlwilson]

• added authors update to postface material;
• versioned the latest PDF METS profile;
• removed unused collatoral; and
• updated the archive to add the 2.2 PDF;
• added project LICENSE file for CC-BY;
• moved docs/_config.yml to site/_config.yml;
• removed old docs dir and duplicate site material; and
• cleaned up .gitignore.

[carlwilson]

@karinbredenberg we should merge this early as we can then pull build and test on my fork as we go.