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.
diff --git a/py/objlist.c b/py/objlist.c
index 829677b..4822c7b 100644
--- a/py/objlist.c
+++ b/py/objlist.c
@@ -38,7 +38,9 @@
     print(env, "]");
 }
 
-static mp_obj_t list_make_new(mp_obj_t type_in, int n_args, const mp_obj_t *args) {
+static mp_obj_t list_make_new(mp_obj_t type_in, uint n_args, uint n_kw, const mp_obj_t *args) {
+    // TODO check n_kw == 0
+
     switch (n_args) {
         case 0:
             // return a new, empty list
@@ -248,19 +250,14 @@
     }
 }
 
-mp_obj_t mp_obj_list_sort(mp_obj_t args, mp_map_t *kwargs) {
-    mp_obj_t *args_items = NULL;
-    uint args_len = 0;
-
-    assert(MP_OBJ_IS_TYPE(args, &tuple_type));
-    mp_obj_tuple_get(args, &args_len, &args_items);
-    assert(args_len >= 1);
-    assert(MP_OBJ_IS_TYPE(args_items[0], &list_type));
-    if (args_len > 1) {
+mp_obj_t mp_obj_list_sort(uint n_args, const mp_obj_t *args, mp_map_t *kwargs) {
+    assert(n_args >= 1);
+    assert(MP_OBJ_IS_TYPE(args[0], &list_type));
+    if (n_args > 1) {
         nlr_jump(mp_obj_new_exception_msg(MP_QSTR_TypeError,
                                           "list.sort takes no positional arguments"));
     }
-    mp_obj_list_t *self = args_items[0];
+    mp_obj_list_t *self = args[0];
     if (self->len > 1) {
         mp_map_elem_t *keyfun = mp_map_lookup(kwargs, MP_OBJ_NEW_QSTR(qstr_from_str_static("key")), MP_MAP_LOOKUP);
         mp_map_elem_t *reverse = mp_map_lookup(kwargs, MP_OBJ_NEW_QSTR(qstr_from_str_static("reverse")), MP_MAP_LOOKUP);
@@ -425,14 +422,6 @@
     return o;
 }
 
-mp_obj_t mp_obj_new_list_reverse(uint n, mp_obj_t *items) {
-    mp_obj_list_t *o = list_new(n);
-    for (int i = 0; i < n; i++) {
-        o->items[i] = items[n - i - 1];
-    }
-    return o;
-}
-
 void mp_obj_list_get(mp_obj_t self_in, uint *len, mp_obj_t **items) {
     mp_obj_list_t *self = self_in;
     *len = self->len;