ScyllaDB release: version 0.19

ScyllaDB version 0.19, an open-source, Apache-Cassandra-compatible NoSQL database, has been released with a focus on stability and bug fixes, alongside several notable updates. This release introduces a program called iotune, which optimizes I/O settings during installation, and implements a formal specification of internal protocols to ensure backward compatibility and facilitate rolling upgrades. Enhancements also include a new I/O scheduler that improves performance on systems with slower disks by balancing requests and a CLI tool named scyllatop for monitoring key metrics. These updates aim to streamline ScyllaDB's performance and prepare it for a GA release in the first quarter of 2016.