support for struct type parameters

- param type conversion properly supports deferred param type resolution
- fixed struct conversion incomplete Subroutine traversal
- struct conversion excludes param types from conversion
- parameters are defaulted to have integer type

test/basic/struct_param.v

@@ -0,0 +1,28 @@
+module Module1 #(parameter N = 1);
+    initial begin
+        $display("$bits(T)=", 3);
+        $display("$bits(t)=", 3);
+        $display("$bits(t.a)=", 1);
+        $display("$bits(t.b)=", 2);
+        $display("$bits(x)=", 1);
+        $display("$bits(y)=", 2);
+        $display("$bits(N)=", 32);
+        $display("N=", N);
+    end
+endmodule
+module Module2 #(parameter N = 1);
+    initial begin
+        $display("$bits(T)=", 11);
+        $display("$bits(t)=", 11);
+        $display("$bits(t.a)=", 5);
+        $display("$bits(t.b)=", 3);
+        $display("$bits(x)=", 5);
+        $display("$bits(y)=", 3);
+        $display("$bits(N)=", 32);
+        $display("N=", N);
+    end
+endmodule
+module top;
+    Module1 #(3) m1();
+    Module2 #(11) m2();
+endmodule