Make highlighter manually bundled and bundle remark-specific resources
on every build. Also, update highlighting style when config is updated.
Fallback to default highlight style when specified style is invalid.
Make config have set and get functions for setting and getting configuration options.
Make SlideshowView only care about config changes affecting ratio option.
Only update document CSS when highlightStyle configuration option changes.
Make slide backgrounds centered, not repeated, and scaled to fit if necessary.