Magazine v6.0.0-alpha.0

• Slight tidy of readme.t.js preamble. See #98.
• Sketch of content cache. See #99.
• Rethinking eviction iterator. See #97.
• Convert to ES6. Closes #97.
• Add chicklets and links to README.md. Closes #94.
• Build with Actions, ship coverage to Codecov. Closes #95. Closes #96.
• Add .npmignore. See #94.
• Update .gitignore. See #94.
• Upgrade proof to 9.0.2. Closes #92.
• Update LICENSE for 2020. Closes #93.

Closes #101.