refactor(core): reorganize project structure and remove legacy code

Major reorganization of the project structure:
- Moved legacy synchronous crawler code to legacy folder
- Removed deprecated CLI and docs manager
- Consolidated version manager into utils.py
- Added CrawlerHub to __init__.py exports
- Fixed type hints in async_webcrawler.py
- Fixed minor bugs in chunking and crawler strategies

BREAKING CHANGE: Removed synchronous WebCrawler, CLI, and docs management functionality. Users should migrate to AsyncWebCrawler.

tests/20241401/test_crawlers.py

@@ -0,0 +1,17 @@
+
+# example_usageexample_usageexample_usage# example_usage.py
+import asyncio
+from crawl4ai.crawlers import get_crawler
+
+async def main():
+    # Get the registered crawler
+    example_crawler = get_crawler("example_site.content")
+    
+    # Crawl example.com
+    result = await example_crawler(url="https://example.com")
+        
+    print(result)
+            
+
+if __name__ == "__main__":
+    asyncio.run(main())