add constructors

Pilz.Cryptography/AESStringCrypter.cs

@@ -53,6 +53,16 @@ namespace Pilz.Cryptography
             set => defaultIV = Convert.FromBase64String(value);
         }
 
+        public AESStringCrypter()
+        {
+        }
+
+        public AESStringCrypter(string key, string iv) : this()
+        {
+            Key = key;
+            IV = iv;
+        }
+
         public string Decrypt(string encryptedValue)
         {
             return DecryptStringFromBytes_Aes(Convert.FromBase64String(encryptedValue), GetKey(), GetIV());