Please add support for AppendTrailingSlash to RouteOptions

[danroth27]

Originally reported by @RehanSaeed in aspnet/Mvc#2691

MVC 5 had the RouteCollection.AppendTrailingSlash setting. Please add the same option under the new RouteOptions and perhaps another option to RemoveTrailingSlash for those who prefer not to have one. This is a requirement for Search Engine Optimization.

services.ConfigureRouting(routeOptions =>
    {
        routeOptions.AppendTrailingSlash = true;
        routeOptions.LowercaseUrls = true;
    });