func (s *prefixPipeline) AssetUrl(name string) (url string, err error) {
	url, err = s.AssetPipeline.AssetUrl(name)
	if err == nil {
		url = s.prefix + url
	}
	return
}
add the prefix when providing urls
package assets
import "net/http"
type AssetPipeline interface {
	http.Handler
	AssetUrl(name string) (string, error)
	AssetContents(name string) ([]byte, error)
}
type prefixPipeline struct {
	AssetPipeline
	prefix string
}