v0.13.1

This is a patch release focused on refining the documentation to make SymbolicAI easier to use and extend.

✨ New & Improved

• Clearer Symbol Concepts: The README and documentation have been significantly improved to better explain the core concept of Syntactic (literal) vs. Semantic (neuro-symbolic) modes for Symbol objects. This should make it easier for new users to get started.
• Updated Custom Engine Guide: The guide for creating a custom engine has been updated to use the more modern GPTXChatEngine, reflecting current best practices.

🔧 Fixes & Changes

• Updated Search Engine Model: The default model for the Perplexity search engine (SEARCH_ENGINE_MODEL) has been updated from llama-3.1-sonar-small-128k-online to sonar.

📖 Documentation

• The main README.md has been rewritten to be more concise and welcoming, with better examples for Symbol and Contract.
• The large table of primitives in the README has been condensed, linking to the full documentation for a cleaner first impression.

Full Changelog: v0.13.0...v0.13.1