Version 4.0.0

Major

• Updated Node.js support to ^12.22.0 || ^14.17.0 || >= 16.0.0.
• Updated dev dependencies, some of which require newer Node.js versions than previously supported.
• Removed ./package from the package exports field; the full package.json filename must be used in a require path.
• Renamed index.mjs to assertSnapshot.mjs and added it to the package exports field.
• Renamed the function snapshot to assertSnapshot.
• Renamed the function assertSnapshot argument 2 snapshotFilePath to snapshotFile, and allow it to also be a file URL instance.
• Added runtime argument type checks.
• Implemented TypeScript types via JSDoc comments.

Patch

• Simplified package scripts.
• Added a package docs-check script that checks the readme API docs are up to date with the source JSDoc.
• Check TypeScript types via a new package types script.
• Also run GitHub Actions CI with Node.js v17, and drop v15.
• Configured Prettier option singleQuote to the default, false.
• Improved tests.
• Documentation tweaks.