support '0' listening port, readme update, showcase added

src/utils/string.go

@@ -1,6 +1,10 @@
 package utils
 
-import "strings"
+import (
+	"net/url"
+	"strconv"
+	"strings"
+)
 
 func CommaSeperatedList(s string) []string {
 	res := strings.Split(s, ",")
@@ -9,3 +13,11 @@ func CommaSeperatedList(s string) []string {
 	}
 	return res
 }
+
+func ExtractPort(fullURL string) (int, error) {
+	url, err := url.Parse(fullURL)
+	if err != nil {
+		return 0, err
+	}
+	return strconv.Atoi(url.Port())
+}