fjall: LSM-based embeddable key-value storage engine written in safe Rust

Fjall is a new key-value storage engine written in Rust. It offers features like thread-safe operations, range searching, automatic maintenance, and built-in compression. Fjall uses a single logical database called a Keyspace, split into partitions for organization. The engine supports multi-threaded access and optional single-writer transactions. While not a standalone server or relational database, Fjall provides flexible durability options and a stable disk format as of version 1.0.0. It's designed for embedding in applications and can handle various workloads efficiently.