feat(crawl4ai): Implement adaptive crawling feature

This commit introduces the adaptive crawling feature to the crawl4ai project. The adaptive crawling feature intelligently determines when sufficient information has been gathered during a crawl, improving efficiency and reducing unnecessary resource usage.

The changes include the addition of new files related to the adaptive crawler, modifications to the existing files, and updates to the documentation. The new files include the main adaptive crawler script, utility functions, and various configuration and strategy scripts. The existing files that were modified include the project's initialization file and utility functions. The documentation has been updated to include detailed explanations and examples of the adaptive crawling feature.

The adaptive crawling feature will significantly enhance the capabilities of the crawl4ai project, providing users with a more efficient and intelligent web crawling tool.

Significant modifications:
- Added adaptive_crawler.py and related scripts
- Modified __init__.py and utils.py
- Updated documentation with details about the adaptive crawling feature
- Added tests for the new feature

BREAKING CHANGE: This is a significant feature addition that may affect the overall behavior of the crawl4ai project. Users are advised to review the updated documentation to understand how to use the new feature.

Refs: #123, #456

docs/md_v2/core/quickstart.md

@@ -272,7 +272,43 @@ if __name__ == "__main__":
 
 ---
 
-## 7. Multi-URL Concurrency (Preview)
+## 7. Adaptive Crawling (New!)
+
+Crawl4AI now includes intelligent adaptive crawling that automatically determines when sufficient information has been gathered. Here's a quick example:
+
+```python
+import asyncio
+from crawl4ai import AsyncWebCrawler, AdaptiveCrawler
+
+async def adaptive_example():
+    async with AsyncWebCrawler() as crawler:
+        adaptive = AdaptiveCrawler(crawler)
+        
+        # Start adaptive crawling
+        result = await adaptive.digest(
+            start_url="https://docs.python.org/3/",
+            query="async context managers"
+        )
+        
+        # View results
+        adaptive.print_stats()
+        print(f"Crawled {len(result.crawled_urls)} pages")
+        print(f"Achieved {adaptive.confidence:.0%} confidence")
+
+if __name__ == "__main__":
+    asyncio.run(adaptive_example())
+```
+
+**What's special about adaptive crawling?**
+- **Automatic stopping**: Stops when sufficient information is gathered
+- **Intelligent link selection**: Follows only relevant links
+- **Confidence scoring**: Know how complete your information is
+
+[Learn more about Adaptive Crawling →](adaptive-crawling.md)
+
+---
+
+## 8. Multi-URL Concurrency (Preview)
 
 If you need to crawl multiple URLs in **parallel**, you can use `arun_many()`. By default, Crawl4AI employs a **MemoryAdaptiveDispatcher**, automatically adjusting concurrency based on system resources. Here’s a quick glimpse: