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

docs/src/docPages/api/marks/italic.md

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+# Italic
+Use this extension to render text in *italic*. If you pass `<em>`, `<i>` tags, or text with inline `style` attributes setting `font-style: italic` in the editor’s initial content, they all will be rendered accordingly.
+
+Type `*one asterisk*` or `_one underline_` and it will magically transform to *italic* text while you type.
+
+::: warning Restrictions
+The extension will generate the corresponding `<em>` HTML tags when reading contents of the `Editor` instance. All text marked italic, regardless of the method will be normalized to `<em>` HTML tags.
+:::
+
+## Installation
+```bash
+# with npm
+npm install @tiptap/extension-italic
+
+# with Yarn
+yarn add @tiptap/extension-italic
+```
+
+## Settings
+| Option | Type   | Default | Description                                  |
+| ------ | ------ | ------- | -------------------------------------------- |
+| class  | string | –       | Add a custom class to the rendered HTML tag. |
+
+## Commands
+| Command | Options | Description       |
+| ------- | ------- | ----------------- |
+| italic  | —       | Mark text italic. |
+
+## Keyboard shortcuts
+* Windows/Linux: `Control`&nbsp;`I`
+* macOS: `Cmd`&nbsp;`I`
+
+## Source code
+[packages/extension-italic/](https://github.com/ueberdosis/tiptap-next/blob/main/packages/extension-italic/)
+
+## Usage
+<demo name="Extensions/Italic" highlight="3-5,17,36" />