Replace bash release helper scripts with Go progam

cmd/gorepomod/internal/utils/utils.go

@@ -0,0 +1,26 @@
+package utils
+
+import (
+	"log"
+	"os"
+)
+
+func DirExists(name string) bool {
+	info, err := os.Stat(name)
+	if os.IsNotExist(err) {
+		return false
+	}
+	return info.IsDir()
+}
+
+func SliceToSet(slice []string) map[string]bool {
+	result := make(map[string]bool)
+	for _, x := range slice {
+		if _, ok := result[x]; ok {
+			log.Fatalf("programmer error - repeated value: %s", x)
+		} else {
+			result[x] = true
+		}
+	}
+	return result
+}