Enhance crawler capabilities and documentation

- Add llm.txt generator
  - Added SSL certificate extraction in AsyncWebCrawler.
  - Introduced new content filters and chunking strategies for more robust data extraction.
  - Updated documentation.

docs/examples/full_page_screenshot_and_pdf_export.md

@@ -39,8 +39,8 @@ async def main():
                     f.write(b64decode(result.screenshot))
             
             # Save PDF
-            if result.pdf_data:
-                pdf_bytes = b64decode(result.pdf_data)
+            if result.pdf:
+                pdf_bytes = b64decode(result.pdf)
                 with open(os.path.join(__location__, "page.pdf"), "wb") as f:
                     f.write(pdf_bytes)