feat(release): prepare v0.4.3 beta release

Prepare the v0.4.3 beta release with major feature additions and improvements:
- Add JsonXPathExtractionStrategy and LLMContentFilter to exports
- Update version to 0.4.3b1
- Improve documentation for dispatchers and markdown generation
- Update development status to Beta
- Reorganize changelog format

BREAKING CHANGE: Memory threshold in MemoryAdaptiveDispatcher increased to 90% and SemaphoreDispatcher parameter renamed to max_session_permit

docs/md_v2/core/markdown-generation.md

@@ -181,7 +181,7 @@ from crawl4ai.content_filter_strategy import LLMContentFilter
 async def main():
     # Initialize LLM filter with specific instruction
     filter = LLMContentFilter(
-        provider="openai/gpt-4",  # or your preferred provider
+        provider="openai/gpt-4o",  # or your preferred provider
         api_token="your-api-token",  # or use environment variable
         instruction="""
         Focus on extracting the core educational content.