Added a calculator test program.

test/calc.slex

@@ -0,0 +1,42 @@
+rule:
+
+number [0-9]+
+plus \+
+minus \-
+multiply \*
+divide \/
+lparen \(
+rparen \)
+whitespace [ \t\r\n]+
+
+mapping:
+
+number number
+plus plus
+minus minus
+multiply multiply
+divide divide
+lparen lparen
+rparen rparen
+
+code:
+
+%c%
+%post_processor
+    if (input->tag == slex_tag_whitespace) {
+        return slex_skip;
+    }
+    *output = input;
+    return slex_continue;
+post_processor%
+
+%c#%
+%post_processor
+            if (Input.Tag == SegmentTag.whitespace)
+            {
+                Output = null!;
+                return PostProcessResult.Skip;
+            }
+            Output = Input;
+            return PostProcessResult.Continue;
+post_processor%