Make VM stack grow upwards, and so no reversed args arrays.

Change state layout in VM so the stack starts at state[0] and grows
upwards.  Locals are at the top end of the state and number downwards.
This cleans up a lot of the interface connecting the VM to C: now all
functions that take an array of Micro Python objects are in order (ie no
longer in reverse).

Also clean up C API with keyword arguments (call_n and call_n_kw
replaced with single call method that takes keyword arguments).  And now
make_new takes keyword arguments.

emitnative.c has not yet been changed to comply with the new order of
stack layout.

py/objmodule.c

@@ -26,7 +26,7 @@ static void module_load_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest) {
     mp_obj_module_t *self = self_in;
     mp_map_elem_t *elem = mp_map_lookup(self->globals, MP_OBJ_NEW_QSTR(attr), MP_MAP_LOOKUP);
     if (elem != NULL) {
-        dest[1] = elem->value;
+        dest[0] = elem->value;
     }
 }