func (c URLsMap) URLs() []string {
	urls := make([]string, 0)
	for _, us := range c {
		for _, u := range us {
			urls = append(urls, u.String())
		}
	}
	sort.Strings(urls)
	return urls
}
URLs returns a list of all URLs.
The returned list is sorted in ascending lexicographical order.
package types
import (
	"fmt"
	"net/url"
	"sort"
	"strings"
)
type URLsMap map[string]URLs
func NewURLsMap(s string) (URLsMap, error) {
	cl := URLsMap{}
	v, err := url.ParseQuery(strings.Replace(s, ",", "&", -1))
	if err != nil {
		return nil, err
	}
	for name, urls := range v {
		if len(urls) == 0 || urls[0] == "" {
			return nil, fmt.Errorf("empty URL given for %q", name)
		}
		us, err := NewURLs(urls)
		if err != nil {
			return nil, err
		}
		cl[name] = us
	}
	return cl, nil
}
func (c URLsMap) String() string {
	pairs := make([]string, 0)
	for name, urls := range c {
		for _, url := range urls {
			pairs = append(pairs, fmt.Sprintf("%s=%s", name, url.String()))
		}
	}
	sort.Strings(pairs)
	return strings.Join(pairs, ",")
}