Enhance Crawl4AI with new features and documentation

- Fix crawler text mode for improved performance; cover missing `srcset` and `data_srcset` attributes in image tags.
  - Introduced Managed Browsers for enhanced crawling experience.
  - Updated documentation for clearer navigation on configuration.
  - Changed 'text_only' to 'text_mode' in configuration and methods.
  - Improved performance and relevance in content filtering strategies.

tests/async/test_0.4.2_config_params.py

@@ -32,7 +32,7 @@ async def test_browser_config_object():
 async def test_browser_performance_config():
     """Test browser configurations focused on performance"""
     browser_config = BrowserConfig(
-        text_only=True,
+        text_mode=True,
         light_mode=True,
         extra_args=['--disable-gpu', '--disable-software-rasterizer'],
         ignore_https_errors=True,