Allow for defining ignored files from assets/ that should not be automatically served #306

I have couple of available color pallets on my site, the app.callback changes the href value of corresponding html.Link when user picks another option. I would like to keep all my styles (default ones + colors defining) in single directory, it would be nice to have some way to define ignored files, of best regexp that will define ignored filename from the assets directory as in case like this including all styles in the <head> will not work.