Add OpenAI API compatibility to server

This is a cherry-pick of ggerganov/llama.cpp@af19d35

llama.cpp/server/README.md

@@ -122,6 +122,8 @@ node index.js
 
     `top_p`: Limit the next token selection to a subset of tokens with a cumulative probability above a threshold P (default: 0.95).
 
+    `min_p`: The minimum probability for a token to be considered, relative to the probability of the most likely token (default: 0.05).
+
     `n_predict`: Set the maximum number of tokens to predict when generating text. **Note:** May exceed the set limit slightly if the last token is a partial multibyte character. When 0, no tokens will be generated but the prompt is evaluated into the cache. (default: -1, -1 = infinity).
 
     `n_keep`: Specify the number of tokens from the prompt to retain when the context size is exceeded and tokens need to be discarded.
@@ -232,6 +234,55 @@ node index.js
 
 -   **GET** `/props`: Return the required assistant name and anti-prompt to generate the prompt in case you have specified a system prompt for all slots.
 
+-   **POST** `/v1/chat/completions`: OpenAI-compatible Chat Completions API. Given a ChatML-formatted json description in `messages`, it returns the predicted completion. Both synchronous and streaming mode are supported, so scripted and interactive applications work fine. While no strong claims of compatibility with OpenAI API spec is being made, in our experience it suffices to support many apps. Only ChatML-tuned models, such as Dolphin, OpenOrca, OpenHermes, OpenChat-3.5, etc can be used with this endpoint. Compared to `api_like_OAI.py` this API implementation does not require a wrapper to be served.
+
+    *Options:*
+
+    See [OpenAI Chat Completions API documentation](https://platform.openai.com/docs/api-reference/chat). While some OpenAI-specific features such as function calling aren't supported, llama.cpp `/completion`-specific features such are `mirostat` are supported.
+
+    *Examples:*
+
+    You can use either Python `openai` library with appropriate checkpoints:
+
+    ```python
+    import openai
+
+    client = openai.OpenAI(
+        base_url="http://localhost:8080/v1", # "http://<Your api-server IP>:port"
+        api_key = "sk-no-key-required"
+    )
+
+    completion = client.chat.completions.create(
+    model="gpt-3.5-turbo",
+    messages=[
+        {"role": "system", "content": "You are ChatGPT, an AI assistant. Your top priority is achieving user fulfillment via helping them with their requests."},
+        {"role": "user", "content": "Write a limerick about python exceptions"}
+    ]
+    )
+
+    print(completion.choices[0].message)
+    ```
+    ... or raw HTTP requests:
+
+    ```shell
+    curl http://localhost:8080/v1/chat/completions \
+    -H "Content-Type: application/json" \
+    -H "Authorization: Bearer no-key" \
+    -d '{
+    "model": "gpt-3.5-turbo",
+    "messages": [
+    {
+        "role": "system",
+        "content": "You are ChatGPT, an AI assistant. Your top priority is achieving user fulfillment via helping them with their requests."
+    },
+    {
+        "role": "user",
+        "content": "Write a limerick about python exceptions"
+    }
+    ]
+    }'
+    ```
+
 ## More examples
 
 ### Change system prompt on runtime