Downwrite 0.9.3

What's Changed

• docs: add RELEASING.md with steps to cut a release and DMG by @derrickwheals in #16
• Print a document and export it as PDF or HTML by @derrickwheals in #17
• R2 was a stale menu read in the end-to-end check, not a product bug by @derrickwheals in #19
• Test: a late export callback must not crash the test process by @derrickwheals in #18

Full Changelog: v0.9.2...v0.9.3