Replace fixed-width `.page` with `max-width`, add `padding` to body, and introduce two breakpoints (639px and 479px) that adjust nav gutter, header centering, and main margin. Convert `.header`, `.content`, `.nav` divs to `<header>`, `<main>`, `<nav>` tags, add viewport meta tag, and hide GitHub ribbon on small screens.
- Delete doc/site/style.css and add doc/site/style.scss with Sass variables, Dosis header font, box-sizing, absolute header positioning, and link hover effects
- Update template.html to reference Dosis font, lowercase nav headings, and change tagline to "a classy little scripting language"
- Add .sass-cache/ to .gitignore and rename Makefile phony target from docs to builtin
- Modify generate_docs.py to compile style.scss via sass subprocess instead of copying static CSS
- Tweak performance.markdown and qa.markdown for minor wording improvements
