Implementing various types and collections from the Rust stdlib.

Worked through using various resources.

• Rustnomicon.
• Jon Gjengset's wonderful youtube series.
• Rust stdlib, for ideas and hints on implementations.
• Learn Rust With Entirely Too Many Linked Lists.
• Rust API Guidelines.

The goal is to learn about unsafe Rust and data structures.

Collections

• [-] crate::Vec.

Interior Mutability & Reference Counts

• Cell
• RefCell
• Rc
• Arc
• Mutex
• RwLock

Async

• Local Executor (!Send + !Sync).