Release 0.4.0

Until version 1.0 (at least) library API is subject to potentially incompatible changes, while the code gets more stable.
However, functionalities from older versions should always be available, with minor code adjustments.

• Refactoring: Endpoint has been renamed AiEndpoint, new Endpoint interface is now just a marker.
• Refactoring: LlmUtil is now ChunkUtil. Methods added to support chunking with moving window and overlapping text.
• EmbeddingService now uses the above methods to embed text in a more flexible way.
• Web Search: SearchEndpoint added. Created GoogleSearchService to provide online search capabilities.
• Added Text to Speech OpenAI API.
• Added support for multiple function calls (tools) in OpenAI chat completion API.
• OpenAI image service now supports DALL-E 3 and uses it by default.
• OpenAiChatService uses GPT-4 8k by default.
• Fixed broken OpenAI audio API (whisper-1 model).
• Added new categories for OpenAI moderation API.
• Added "slot filling" capabilities to CompletionService and ChatService.
• Robustness: Added automatic "throttling" when API call rate limit is exceeded (automatic handling of HTTP errors 429, 500 & 503).
• Robustness: Added automatic adjustment of completion size for OpenAI completion services when context size is exceeded.
• Added extensive example (EssayWriter).
• Bug fixes.