Azure.Messaging.EventHubs 5.1.0-preview.1

### Acknowledgments Thank you to our developer community members who helped to make the Event Hubs client libraries better with their contributions to this release: - Alberto De Natale _([GitHub](https://github.com/albertodenatale))_ - Christopher Scott _([GitHub](https://github.com/christothes))_ #### Consuming events - A new primitive, `EventProcessor<TPartition>`, has been implemented to serve as an extensibility point for creating a custom event processor instance. It offers built-in fault tolerance, load balancing, and structure while allowing tuning for low-level network configuration, processing of events in batches, and customization for the storage of checkpoints. More detail can be found in the [design proposal](https://github.com/Azure/azure-sdk-for-net/blob/master/sdk/eventhub/Azure.Messaging.EventHubs/design/event-processor%7BT%7D-proposal.md). - A new primitive, `PartitionProcessor`, has been implemented to serve as a low-level means of reading batches of events from a single partition with greater control over network configuration. More detail can be found in the [design proposal](https://github.com/Azure/azure-sdk-for-net/blob/master/sdk/eventhub/Azure.Messaging.EventHubs/design/partition-receiver-proposal.md). #### Publishing events - Event batches are now protected against modification while publishing is actively taking place. #### Bug fixes and foundation - Exceptions surfaced will now properly remember their context in all scenarios; previously, some deferred cases unintentionally reset the context. - Validation for the Event Hubs fully qualified namespace has been improved, allowing for more deterministic failures when creating clients. - The diagnostic scope for activities will now complete in a more deterministic manner. (A community contribution, courtesy of [christothes]((https://github.com/christothes))) - Diagnostic activities have been extended with additional information about events being processed and with additional environmental context. - Parsing of connection strings is now more permissive for the `Endpoint` key, allowing additional formats that result from common mistakes when building the string rather than copying the value from the portal. - `LastEnqueuedEventProperties` can now be compared for structural equality. #### Testing - For special cases, the live tests may be instructed to use existing Azure resources instead of dynamically creating dedicated resources for the run. (A community contribution, courtesy of [albertodenatale](https://github.com/albertodenatale)) https://github.com/Azure/azure-sdk-for-net/blob/e85d6412c147037eeae098c76ca30ba1968882f6/sdk/eventhub/Azure.Messaging.EventHubs/CHANGELOG.md