_mean = function(values) {
        var result = 0,
            valuesLength = values.length;
        for (var i = 0; i < valuesLength; i += 1) {
            result += values[i];
        }
        return (result / valuesLength) || 0;
    }
Alias for `Runner.run`.
@method start
@param {runner} runner
@param {engine} engine