moductypes: Foreign data interface module, roughly based on ctype ideas.

But much smaller and memory-efficient. Uses Python builtin data structures
(dict, tuple, int) to describe structure layout.
diff --git a/py/compile.c b/py/compile.c
index c5f2166..e89554a 100644
--- a/py/compile.c
+++ b/py/compile.c
@@ -104,6 +104,9 @@
 }
 
 STATIC const mp_map_elem_t mp_constants_table[] = {
+    #if MICROPY_PY_UCTYPES
+    { MP_OBJ_NEW_QSTR(MP_QSTR_uctypes), (mp_obj_t)&mp_module_uctypes },
+    #endif
     // Extra constants as defined by a port
     MICROPY_PORT_CONSTANTS
 };