Slightly re-structure exercise code

    constructor(name, index, execute) {

        this.name = name

        this.index = index

        // Bind the execute function to the ExerciseExecutionContext.

        // This means that the `this` keyword, when used in the function, will

        // point to this ExerciseExecutionContext object.

        this.#execute = execute.bind(this.#context)

        this.#execute = execute

    }

    /**

     * Start the exercise.

     */

    start() {

        this.#execute()

        // Bind the execute function to the ExerciseExecutionContext.

        // This means that the `this` keyword, when used in the function, will

        // point to this ExerciseExecutionContext object.

        // The newly bound function is then called.

        this.#execute.bind(this.#context)()

    }

    /**