Issue #102

Today I was reading the project in IGListKit Tutorial: Better UICollectionViews, I encounter something I often overlook

let nav = UINavigationController(navigationBarClass: CustomNavigationBar.self, toolbarClass: nil)
nav.pushViewController(FeedViewController(), animated: false)

So we can provide custom navigationBarClass and toolbarClass for UINavigationController. This RRMaterialNavigationBar also has cool implementation of a material UINavigationBar.

Together with UINavigationBarDelegate we can do some cool things