feat: minify html and various improvements

[SethFalco]

A general revamp of the theme.

• Minify the HTML before writing to a file.
• Add the html[lang] attribute to the document, and expect language codes in the languages section instead of language names.
• When displaying languages, use the JavaScript Intl API instead of accepting literal strings.
• When displaying links, only display the domain rather than the whole URL. i.e. https://example.org/ → example.org
• For the Twitter card logic, also accept a social media network named "x".
• Clean up CSS and remove the standard reset in favor of our own.
• Remove unused classes from the Handlebars template.
• Updates font-family to include more fonts across operating systems.

Chores

• Include a JSON Resume fixture that can be used for test builds and the preview.
• Add GitHub action to test build before merging PRs. (Currently just runs build:* rather than unit tests.)
• Fix a typo in the README.