An efficient unordered dynamically-sized data structure.

• k - original capacity

• Due to compaction on removal, this is essentially disregarded, resulting in incredibly fast iteration.

• atomic - uses std::sync::Arc instead of the default std::rc::Rc for thread safety.
• clone - allows ValueIndex to be cloneable, allowing for greater versatility.
• get (default) - Obtain a reference from the bucket at the indexed position.