py: Add attrtuple object, for space-efficient tuples with attr access.

If you need the functionality of a namedtuple but will only make 1 or a
few instances, then use an attrtuple instead.
diff --git a/py/mpconfig.h b/py/mpconfig.h
index a403a66..df18290 100644
--- a/py/mpconfig.h
+++ b/py/mpconfig.h
@@ -502,6 +502,12 @@
 #define MICROPY_PY_ARRAY_SLICE_ASSIGN (0)
 #endif
 
+// Whether to support attrtuple type (MicroPython extension)
+// It provides space-efficient tuples with attribute access
+#ifndef MICROPY_PY_ATTRTUPLE
+#define MICROPY_PY_ATTRTUPLE (1)
+#endif
+
 // Whether to provide "collections" module
 #ifndef MICROPY_PY_COLLECTIONS
 #define MICROPY_PY_COLLECTIONS (1)