Change some parts of the core API to use mp_uint_t instead of uint/int.

Addressing issue #50, still some way to go yet.
diff --git a/py/objint_longlong.c b/py/objint_longlong.c
index 466b45c..c4c1613 100644
--- a/py/objint_longlong.c
+++ b/py/objint_longlong.c
@@ -73,7 +73,7 @@
     return self->val >= 0;
 }
 
-mp_obj_t mp_obj_int_unary_op(int op, mp_obj_t o_in) {
+mp_obj_t mp_obj_int_unary_op(mp_uint_t op, mp_obj_t o_in) {
     mp_obj_int_t *o = o_in;
     switch (op) {
         case MP_UNARY_OP_BOOL: return MP_BOOL(o->val != 0);
@@ -84,7 +84,7 @@
     }
 }
 
-mp_obj_t mp_obj_int_binary_op(int op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
+mp_obj_t mp_obj_int_binary_op(mp_uint_t op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
     long long lhs_val;
     long long rhs_val;