Refactor video-util.ts and rename markdown-preview (#233)

* Refactor video-util.ts
* Rename markdown-preview to markdown-renderer and refactor some methods

Signed-off-by: Tilman Vatteroth <tilman.vatteroth@tu-dortmund.de>

src/components/editor/markdown-renderer/regex-plugins/replace-pdf-short-code.ts

@@ -0,0 +1,11 @@
+import { RegexOptions } from '../../../../external-types/markdown-it-regex/interface'
+
+export const replacePdfShortCode: RegexOptions = {
+  name: 'pdf-short-code',
+  regex: /^{%pdf (.*) ?%}$/,
+  replace: (match) => {
+    // ESLint wants to collapse this tag, but then the tag won't be valid html anymore.
+    // noinspection CheckTagEmptyBody
+    return `<codimd-pdf url="${match}"></codimd-pdf>`
+  }
+}