Initial implementation of slider

Single-file markdown slideshow for the terminal. Parses slides split by
`---`, renders each with glow, and navigates with n/p/q or arrow keys.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

examples/presentation.md

@@ -0,0 +1,56 @@
+# Welcome to the Presentation
+
+## Slide 1: Introduction
+
+This is a simple slide to demonstrate `glow`'s capabilities.
+
+### Features Showcase
+
+- **Code Blocks**:
+
+  ```python
+  def greet(name):
+      print(f"Hello, {name}!")
+  ```
+
+- **Tables**:
+
+  | Feature        | Description         |
+  |----------------|---------------------|
+  | Syntax Highlighting | Supports Python, JavaScript, etc. |
+  | Tables          | Easy to read and format |
+  | Markdown        | Full markdown support |
+
+- **Inline Code**:
+  `glow` supports inline code like `print("Hello")`.
+
+---
+
+# Slide 2: Advanced Features
+
+## Code Blocks with Line Numbers
+
+```bash
+#!/bin/bash
+echo "This is a bash script."
+```
+
+## Tables with Markdown
+
+| Column 1 | Column 2 |
+|----------|----------|
+| Data 1   | Data 2   |
+| Data 3   | Data 4   |
+
+## Emoji and Formatting
+
+:smile: This is a smiley!
+**Bold text** and *italic text* are supported.
+
+---
+
+# Slide 3: Conclusion
+
+## Thank You
+
+This is the final slide. Press `q` to exit.