public static void threadPool(int maxThreads, int minThreads, int idleTimeoutMillis) {
        getInstance().threadPool(maxThreads, minThreads, idleTimeoutMillis);
    }
Configures the embedded web server's thread pool.

@param maxThreads        max nbr of threads.
@param minThreads        min nbr of threads.
@param idleTimeoutMillis thread idle timeout (ms).
src/main/java/spark/Spark.java