Function addition

cranelift/interpreter/src/environment.rs:83–90

()

    #[test]
    fn addition() {
        let mut env = FunctionStore::default();
        let a = "a";
        let f = Function::new();

        env.add(a.to_string(), &f);
        assert!(env.get_by_name(a).is_some());
    }

    #[test]
    fn nonexistence() {