Added expression function for DateTime.MinValue

InABox.Core/Expression/DateFunctions.cs

@@ -12,6 +12,7 @@ namespace InABox.Core
         {
             CoreExpression.RegisterFunction("Now", "Returns the current date and time.", GROUP, new string[] {}, (p, vars, c) => DateTime.Now);
             CoreExpression.RegisterFunction("Today", "Returns the current date.", GROUP, new string[] {}, (p, vars, c) => DateTime.Today);
+            CoreExpression.RegisterFunction("DateTime_MinValue", "Returns the minimum value for a date and time.", GROUP, new string[] {}, (p, vars, c) => DateTime.MinValue);
         }
     }
 }