Upgrade to Eleventy 3.0, transition JavaScript to ESM

[querkmachine]

Finishes what #71 started. Closes #35.

Changes

• Updates the Eleventy dependency to the latest 3.0 canary release.
• Sets the package type to "module" so that files are expected to be ESM format.
• Updates all build, configuration and data related files from CommonJS to ESM format.

Additionally

• Renames the configuration file from .eleventy.js to eleventy.config.js.
• Changes the global paths.json file to ESM formatted JS and renames it paths.js for ease of use in ESM. assert/with declarations are still considered experimental by node.
• Changes the about section's 11tydata file (about.json) to ESM formatted JS and renames it about.11tydata.js, for consistency with other 11tydata files.
• Fixes a front matter parsing issue that hasn't been flagged before. Seemingly this is because of stricter checks on YAML formatting in Eleventy 3.0 or it's dependencies.