December update for Azure IoT Edge

The December update of Azure IoT Edge includes the following improvements: * You can now write modules in C by using the [C client SDK](https://github.com/Azure/azure-iot-sdk-c/tree/modules-preview). * Azure IoT Edge features are now available in national clouds. IoT Edge runtime improvements: * We fixed a bug that prevented the edge hub from multiplexing connections between an edge device and Azure IoT Hub. * Communication with IoT Hub falls back to AMQP over WebSockets if AMQP port 5671 is blocked. * Messages that have not been delivered to the cloud due to a temporary internet connection are now persisted to storage Azure Resource Manager devices. * Deployments with critical errors can fail instead of retrying forever. * We added support for WSL. Azure portal fixes specific to IoT Edge: * We added advanced settings to allow customers to override the edge agent image, edge hub image, and storeAndForwardConfiguration timeToLiveSecs value. * We fixed a bug that prevented many special characters from being used in the target condition of a deployment. * We added the deployment status for the modules: pending deployment, pending modification, pending removal, and deployed. Documentation: * We added a [troubleshooting guide](https://docs.microsoft.com/en-us/azure/iot-edge/troubleshoot). * We added an article on [how to migrate from V1 to V2](https://github.com/Azure/iot-edge/blob/master/v1/doc/migration%5Ffrom%5Fv1%5Fto%5Fv2.md). * We updated[ target condition syntax](https://docs.microsoft.com/en-us/azure/iot-edge/module-deployment-monitoring#target-condition). * We updated the [Deploy Azure Machine Learning tutorial](https://docs.microsoft.com/en-us/azure/iot-edge/tutorial-deploy-machine-learning) to show how to build a machine learning model. ​ * Internet of Things * Features * [ Internet of Things](https://azure.microsoft.com/en-gb/products/iot-hub/)