move nodes and marks to a separate folder, add missing extensions

docs/src/docPages/api/nodes/horizontal-rule.md

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+# HorizontalRule
+Use this extension to render a `<hr>` HTML tag. If you pass `<hr>` in the editor’s initial content, it’ll be rendered accordingly.
+
+Type three dashes (<code>---</code>) or three underscores and a space (<code>___ </code>) at the beginning of a new line and it will magically transform to a horizontal rule.
+
+## Installation
+```bash
+# with npm
+npm install @tiptap/extension-horizontal-rule
+
+# with Yarn
+yarn add @tiptap/extension-horizontal-rule
+```
+
+## Settings
+| Option | Type   | Default | Description                                  |
+| ------ | ------ | ------- | -------------------------------------------- |
+| class  | string | –       | Add a custom class to the rendered HTML tag. |
+
+## Commands
+| Command         | Options | Description               |
+| --------------- | ------- | ------------------------- |
+| horizontalRule | —       | Create a horizontal rule. |
+
+## Keyboard shortcuts
+*None*
+
+## Source code
+[packages/extension-horizontal-rule/](https://github.com/ueberdosis/tiptap-next/blob/main/packages/extension-horizontal-rule/)
+
+## Usage
+<demo name="Extensions/HorizontalRule" highlight="3-5,17,36" />