change code structure

test/filesystem.nas

@@ -0,0 +1,12 @@
+import("lib.nas");
+
+var fd=io.open("test/filesystem.nas");
+while((var line=io.readln(fd))!=nil)
+    println(line);
+io.close(fd);
+println(io.stat("test/filesystem.nas"));
+
+var dd=unix.opendir("test");
+while((var name=unix.readdir(dd))!=nil)
+    println(name);
+unix.closedir(dd);