added DateTimeToUnixTimestamp helper

SweetLib/Utils/SweetUtils.cs

@@ -39,5 +39,15 @@ namespace SweetLib.Utils
 
             return invalidChars.Aggregate(fileName, (current, c) => current.Replace(c, replaceChar));
         }
+
+        /// <summary>
+        /// Converts a <see cref="DateTime"/> into an Unix timestamp.
+        /// </summary>
+        /// <param name="date"><see cref="DateTime"/> to convert into Unix timestamp.</param>
+        /// <returns>Converted Unix timestamp</returns>
+        public static double DateTimeToUnixTimeStamp(DateTime date)
+        {
+            return date.Subtract(new DateTime(1970, 1, 1)).TotalSeconds;
+        }
     }
 }