py: Make tuple and list use mp_int_t/mp_uint_t.

Part of code cleanup, to resolve issue #50.
diff --git a/py/objlist.c b/py/objlist.c
index fb151f8..59390f3 100644
--- a/py/objlist.c
+++ b/py/objlist.c
@@ -36,8 +36,8 @@
 #include "runtime.h"
 #include "objlist.h"
 
-STATIC mp_obj_t mp_obj_new_list_iterator(mp_obj_list_t *list, int cur);
-STATIC mp_obj_list_t *list_new(uint n);
+STATIC mp_obj_t mp_obj_new_list_iterator(mp_obj_list_t *list, mp_uint_t cur);
+STATIC mp_obj_list_t *list_new(mp_uint_t n);
 STATIC mp_obj_t list_extend(mp_obj_t self_in, mp_obj_t arg_in);
 STATIC mp_obj_t list_pop(mp_uint_t n_args, const mp_obj_t *args);
 
@@ -50,7 +50,7 @@
 STATIC void list_print(void (*print)(void *env, const char *fmt, ...), void *env, mp_obj_t o_in, mp_print_kind_t kind) {
     mp_obj_list_t *o = o_in;
     print(env, "[");
-    for (int i = 0; i < o->len; i++) {
+    for (mp_uint_t i = 0; i < o->len; i++) {
         if (i > 0) {
             print(env, ", ");
         }
@@ -188,7 +188,7 @@
             return res;
         }
 #endif
-        uint index_val = mp_get_index(self->base.type, self->len, index, false);
+        mp_uint_t index_val = mp_get_index(self->base.type, self->len, index, false);
         return self->items[index_val];
     } else {
 #if MICROPY_PY_BUILTINS_SLICE
@@ -271,7 +271,7 @@
     if (self->len == 0) {
         nlr_raise(mp_obj_new_exception_msg(&mp_type_IndexError, "pop from empty list"));
     }
-    uint index = mp_get_index(self->base.type, self->len, n_args == 1 ? MP_OBJ_NEW_SMALL_INT(-1) : args[1], false);
+    mp_uint_t index = mp_get_index(self->base.type, self->len, n_args == 1 ? MP_OBJ_NEW_SMALL_INT(-1) : args[1], false);
     mp_obj_t ret = self->items[index];
     self->len -= 1;
     memmove(self->items + index, self->items + index + 1, (self->len - index) * sizeof(mp_obj_t));
@@ -286,7 +286,7 @@
 
 // TODO make this conform to CPython's definition of sort
 STATIC void mp_quicksort(mp_obj_t *head, mp_obj_t *tail, mp_obj_t key_fn, bool reversed) {
-    int op = reversed ? MP_BINARY_OP_MORE : MP_BINARY_OP_LESS;
+    mp_uint_t op = reversed ? MP_BINARY_OP_MORE : MP_BINARY_OP_LESS;
     while (head < tail) {
         mp_obj_t *h = head - 1;
         mp_obj_t *t = tail;
@@ -442,7 +442,7 @@
     .locals_dict = (mp_obj_t)&list_locals_dict,
 };
 
-void mp_obj_list_init(mp_obj_list_t *o, uint n) {
+void mp_obj_list_init(mp_obj_list_t *o, mp_uint_t n) {
     o->base.type = &mp_type_list;
     o->alloc = n < LIST_MIN_ALLOC ? LIST_MIN_ALLOC : n;
     o->len = n;
@@ -450,29 +450,29 @@
     mp_seq_clear(o->items, n, o->alloc, sizeof(*o->items));
 }
 
-STATIC mp_obj_list_t *list_new(uint n) {
+STATIC mp_obj_list_t *list_new(mp_uint_t n) {
     mp_obj_list_t *o = m_new_obj(mp_obj_list_t);
     mp_obj_list_init(o, n);
     return o;
 }
 
-mp_obj_t mp_obj_new_list(uint n, mp_obj_t *items) {
+mp_obj_t mp_obj_new_list(mp_uint_t n, mp_obj_t *items) {
     mp_obj_list_t *o = list_new(n);
     if (items != NULL) {
-        for (int i = 0; i < n; i++) {
+        for (mp_uint_t i = 0; i < n; i++) {
             o->items[i] = items[i];
         }
     }
     return o;
 }
 
-void mp_obj_list_get(mp_obj_t self_in, uint *len, mp_obj_t **items) {
+void mp_obj_list_get(mp_obj_t self_in, mp_uint_t *len, mp_obj_t **items) {
     mp_obj_list_t *self = self_in;
     *len = self->len;
     *items = self->items;
 }
 
-void mp_obj_list_set_len(mp_obj_t self_in, uint len) {
+void mp_obj_list_set_len(mp_obj_t self_in, mp_uint_t len) {
     // trust that the caller knows what it's doing
     // TODO realloc if len got much smaller than alloc
     mp_obj_list_t *self = self_in;
@@ -481,7 +481,7 @@
 
 void mp_obj_list_store(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
     mp_obj_list_t *self = self_in;
-    uint i = mp_get_index(self->base.type, self->len, index, false);
+    mp_uint_t i = mp_get_index(self->base.type, self->len, index, false);
     self->items[i] = value;
 }
 
@@ -512,7 +512,7 @@
     .iternext = list_it_iternext,
 };
 
-mp_obj_t mp_obj_new_list_iterator(mp_obj_list_t *list, int cur) {
+mp_obj_t mp_obj_new_list_iterator(mp_obj_list_t *list, mp_uint_t cur) {
     mp_obj_list_it_t *o = m_new_obj(mp_obj_list_it_t);
     o->base.type = &mp_type_list_it;
     o->list = list;