Rust example: hello world and fibonacci

Run a Rust program that prints Hello World and computes Fibonacci numbers.

A minimal Rust program whose fn main() prints a greeting with the println! macro, then loops over the range 0..10 printing each Fibonacci number. The fib function takes a u64 and returns a u64, using Rust's expression-based if/else (no return keyword) to yield n for the base case or the sum of the two previous values otherwise.