This PR:

• Initiates the repo as a Rust crate
• Adds the ash::node module with the AshNode struct that allows interacting with the node's ID easily
• Adds unit tests for ash::node

Note: I chose to keep 2 functions (from_cb58_id + from_bytes_id) for constructing an AshNode from a node's ID rather than implementing a trait like TryFrom (and having a single try_from function). It was making the code too complicated IMO.