Extend supported variables and improve parser errors

Sharp7.Rx/Exceptions/S7Exception.cs

@@ -0,0 +1,27 @@
+namespace Sharp7.Rx;
+
+public abstract class S7Exception : Exception
+{
+    protected S7Exception(string message) : base(message)
+    {
+    }
+
+    protected S7Exception(string message, Exception innerException) : base(message, innerException)
+    {
+    }
+}
+
+public class InvalidS7AddressException : S7Exception
+{
+    public InvalidS7AddressException(string message, string input) : base(message)
+    {
+        Input = input;
+    }
+
+    public InvalidS7AddressException(string message, Exception innerException, string input) : base(message, innerException)
+    {
+        Input = input;
+    }
+
+    public string Input { get; private set; }
+}