py: Convert [u]int to mp_[u]int_t where appropriate.

Addressing issue #50.
diff --git a/py/binary.h b/py/binary.h
index 5f577da..2a63ba9 100644
--- a/py/binary.h
+++ b/py/binary.h
@@ -29,9 +29,9 @@
 #define BYTEARRAY_TYPECODE 0
 
 int mp_binary_get_size(char struct_type, char val_type, mp_uint_t *palign);
-mp_obj_t mp_binary_get_val_array(char typecode, void *p, int index);
-void mp_binary_set_val_array(char typecode, void *p, int index, mp_obj_t val_in);
-void mp_binary_set_val_array_from_int(char typecode, void *p, int index, mp_int_t val);
+mp_obj_t mp_binary_get_val_array(char typecode, void *p, mp_uint_t index);
+void mp_binary_set_val_array(char typecode, void *p, mp_uint_t index, mp_obj_t val_in);
+void mp_binary_set_val_array_from_int(char typecode, void *p, mp_uint_t index, mp_int_t val);
 mp_obj_t mp_binary_get_val(char struct_type, char val_type, byte **ptr);
 void mp_binary_set_val(char struct_type, char val_type, mp_obj_t val_in, byte **ptr);
 long long mp_binary_get_int(mp_uint_t size, bool is_signed, bool big_endian, byte *p);