feat: automatically detect dark theme

feat: add loading animation

feat: add table css, fix egoist#13

fix(style): task list

fix(style): don't use fixed height for toc item

fix: add base option and use it as title link

fix: set root to empty string

fix: change scroll position when heading is visible

fix: use throttle instead of debounce, closes egoist#17

chore: fix typo in docs (egoist#15)

- Change "Hightlight" to "Highlight"