- Set consistent line-height (18.2px) across linenos, code box, and hljs
- Fix linenos z-index to ensure visibility
- Remove padding from hljs to align with line numbers
- Add user-select: none to prevent selecting line numbers
* restructured JavaScript using backbone.js
* replaced highlight.js with CodeMirror for its editor
* added CodeMirror Solarized (dark) theme based on Ethan Schoonover's solarized.vim
* changed `POST /document` to accept real JSON
* cleaned up template and stylesheet