* BUGFIX
  * optimize resource loading
  * refactor expand shortcode to use valid html
  * fix formatting of nested shortcodes markdown
* INTERNAL
  * add markdown linting to CI (markdownlint-cli)
  * add spellchecking to CI (spellcheck-cli)
  * add html/css validation to CI (nu.validator)
  * add page validation to CI (lighthouse-ci)
  * add broken link check to CI (broken-link-checker)
