added source trace comments

- Trace comments cover module items, decls, and stmts
- Added pseudo-lexer to Alex parser for monadic Position production
- Added Position to every DeclToken
- Removed Comment PackageItem
- Added CommentStmt and CommentDecl
- Fixed traversal skipping outer MIAttr ModuleItems
- Generally cleaned up Parser modules

test/basic/inc.sv

@@ -4,4 +4,18 @@ module top;
         x++;
         $display(x);
     end
+    initial begin
+        ++x;
+        $display(x);
+    end
+    initial begin
+        repeat (0);
+        x++;
+        $display(x);
+    end
+    initial begin
+        repeat (0);
+        ++x;
+        $display(x);
+    end
 endmodule

test/basic/inc.v

@@ -1,6 +1,6 @@
 module top;
     integer x = 0;
-    initial begin
+    initial repeat (4) begin
         x = x + 1;
         $display(x);
     end