add twilio-chatbot example with README.md info how to start app

created twilio_websocket_service.py, TwilioFrameSerializer.py

moved pcm_16000_to_ulaw_8000 and ulaw_8000_to_pcm_16000 to src/pipecat/utils/audio.py
fixed callback on disconnect

examples/twilio-chatbot/README.md

@@ -0,0 +1,94 @@
+# Twilio Chatbot
+
+This project is a FastAPI-based chatbot that integrates with Twilio to handle WebSocket connections and provide real-time communication. The project includes endpoints for starting a call and handling WebSocket connections.
+
+## Table of Contents
+
+- [Features](#features)
+- [Requirements](#requirements)
+- [Installation](#installation)
+- [Running the Application](#running-the-application)
+- [Usage](#usage)
+
+## Features
+
+- **FastAPI**: A modern, fast (high-performance), web framework for building APIs with Python 3.6+.
+- **WebSocket Support**: Real-time communication using WebSockets.
+- **CORS Middleware**: Allowing cross-origin requests for testing.
+- **Dockerized**: Easily deployable using Docker.
+
+## Requirements
+
+- Python 3.10
+- Docker (for containerized deployment)
+- ngrok (for tunneling)
+- Twilio Account
+
+## Installation
+
+1. **Set up a virtual environment** (optional but recommended):
+    ```sh
+    python -m venv venv
+    source venv/bin/activate  # On Windows, use `venv\Scripts\activate`
+    ```
+
+2. **Install dependencies**:
+    ```sh
+    pip install -r requirements.txt
+    ```
+
+3. **Create .env**:
+    create .env based on .env.example
+
+4. **Install ngrok**:
+    Follow the instructions on the [ngrok website](https://ngrok.com/download) to download and install ngrok.
+
+## Running the Application
+
+### Using Python
+
+1. **Run the FastAPI application**:
+    ```sh
+    python server.py
+    ```
+
+2. **Start ngrok**:
+    In a new terminal, start ngrok to tunnel the local server:
+    ```sh
+    ngrok http 8765
+    ```
+
+3. **Update the Twilio Webhook**:
+    Copy the ngrok URL and update your Twilio phone number webhook URL to `http://<ngrok_url>/start_call`.
+
+3. **Update the streams.xml**:
+    Copy the ngrok URL and update your .xml URL to `wss://<ngrok_url>/ws`.
+
+### Using Docker
+
+1. **Build the Docker image**:
+    ```sh
+    docker build -t twilio-chatbot .
+    ```
+
+2. **Run the Docker container**:
+    ```sh
+    docker build -t twilio-chatbot .                               
+    docker run -it --rm -p 8765:8765 twilio-chatbot
+    ```
+
+3. **Start ngrok**:
+    In a new terminal, start ngrok to tunnel the local server:
+    ```sh
+    ngrok http 8765
+    ```
+
+4. **Update the Twilio Webhook**:
+    Copy the ngrok URL and update your Twilio phone number webhook URL to `http://<ngrok_url>/start_call`.
+
+5. **Update the streams.xml**:
+    Copy the ngrok URL and update your .xml URL to `wss://<ngrok_url>/ws`.
+
+## Usage
+
+To start a call, simply make a call to your Twilio phone number. The webhook URL will direct the call to your FastAPI application, which will handle it accordingly.