Basic markdown renderer (#197)

* Add basic markdown it rendering
* Add markdown preview
* Add embedings for vimeo, youtube, gist
* Add support for legacy shortcodes and link detection
* Set "both" as editor default
* Add markdown-it-task-lists
* Add twemoji
* Changed SlideShare short-code behaviour from embedding to generating a link
* Extract markdown it parser debugger into separate component
* Deactivate markdown it linkify for now
* Add link safety attributes
* Add one-click-embedding component and use it
* Added embedding changes and deprecations to CHANGELOG.md

Signed-off-by: Tilman Vatteroth <tilman.vatteroth@tu-dortmund.de>
Co-authored-by: Philip Molares <philip@mauricedoepke.de>
Co-authored-by: Erik Michelson <github@erik.michelson.eu>

src/external-types/markdown-it-emoji/index.d.ts

@@ -0,0 +1,6 @@
+
+declare module 'markdown-it-emoji' {
+  import MarkdownIt from 'markdown-it/lib'
+  const markdownItEmoji: MarkdownIt.PluginSimple
+  export = markdownItEmoji
+}

src/external-types/markdown-it-regex/index.d.ts

@@ -0,0 +1,6 @@
+declare module 'markdown-it-regex' {
+  import MarkdownIt from 'markdown-it/lib'
+  import { RegexOptions } from './interface'
+  const markdownItRegex: MarkdownIt.PluginWithOptions<RegexOptions>
+  export = markdownItRegex
+}

src/external-types/markdown-it-regex/interface.ts

@@ -0,0 +1,5 @@
+export interface RegexOptions {
+  name: string,
+  regex: RegExp,
+  replace: (match: string) => string
+}

src/external-types/markdown-it-task-lists/index.d.ts

@@ -0,0 +1,6 @@
+
+declare module 'markdown-it-task-lists' {
+  import MarkdownIt from 'markdown-it/lib'
+  const markdownItTaskLists: MarkdownIt.PluginSimple
+  export = markdownItTaskLists
+}