py: Add MP_ROM_* macros and mp_rom_* types and use them.
diff --git a/py/modio.c b/py/modio.c
index 96572f5..e1c51b9 100644
--- a/py/modio.c
+++ b/py/modio.c
@@ -31,20 +31,20 @@
 extern const mp_obj_type_t mp_type_fileio;
 extern const mp_obj_type_t mp_type_textio;
 
-STATIC const mp_map_elem_t mp_module_io_globals_table[] = {
-    { MP_OBJ_NEW_QSTR(MP_QSTR___name__), MP_OBJ_NEW_QSTR(MP_QSTR__io) },
+STATIC const mp_rom_map_elem_t mp_module_io_globals_table[] = {
+    { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR__io) },
     // Note: mp_builtin_open_obj should be defined by port, it's not
     // part of the core.
-    { MP_OBJ_NEW_QSTR(MP_QSTR_open), (mp_obj_t)&mp_builtin_open_obj },
+    { MP_ROM_QSTR(MP_QSTR_open), MP_ROM_PTR(&mp_builtin_open_obj) },
     #if MICROPY_PY_IO_FILEIO
-    { MP_OBJ_NEW_QSTR(MP_QSTR_FileIO), (mp_obj_t)&mp_type_fileio },
+    { MP_ROM_QSTR(MP_QSTR_FileIO), MP_ROM_PTR(&mp_type_fileio) },
     #if MICROPY_CPYTHON_COMPAT
-    { MP_OBJ_NEW_QSTR(MP_QSTR_TextIOWrapper), (mp_obj_t)&mp_type_textio },
+    { MP_ROM_QSTR(MP_QSTR_TextIOWrapper), MP_ROM_PTR(&mp_type_textio) },
     #endif
     #endif
-    { MP_OBJ_NEW_QSTR(MP_QSTR_StringIO), (mp_obj_t)&mp_type_stringio },
+    { MP_ROM_QSTR(MP_QSTR_StringIO), MP_ROM_PTR(&mp_type_stringio) },
     #if MICROPY_PY_IO_BYTESIO
-    { MP_OBJ_NEW_QSTR(MP_QSTR_BytesIO), (mp_obj_t)&mp_type_bytesio },
+    { MP_ROM_QSTR(MP_QSTR_BytesIO), MP_ROM_PTR(&mp_type_bytesio) },
     #endif
 };