Write up developer release checklist

[hollasch]

Off the top of my head, in rough order:

• Update release checklist if this is incomplete.
• Run final tests.
• Run progression on all involved books for major and possibly minor level releases.
• Review all changes and update changelog. Add summary at the top.
• Update date and version information in all books.
• Update project README.
• Generate PDF versions of the books for release page.
• Merge development branch into release.
• Update main web page (index.html).
• Create Git tag on official tip.
• Create new release on GitHub, referencing the release tag. Attach book PDFs.
• Send out announcements.

Post Release:

• Update development branch with any outstanding changes. (All below reference the new dev branch.)
• In dev, create new section at the top of the CHANGELOG for the next release.
• Update books with stubbed out dates and version information.