libyang FEATURE introduce and use new ly_bool type

To indicate simple flags or true/false return values, use a standalone
ly_bool type.

We do not use stdbool's bool type to avoid need to mimic all its
features on platforms that do not provide it. ly_bool is just a simple
rename for uint8_t and the reason to use it is only a better readability
of the meaning of the variables or function's return values.
diff --git a/src/tree_data_hash.c b/src/tree_data_hash.c
index 177a394..482ce15 100644
--- a/src/tree_data_hash.c
+++ b/src/tree_data_hash.c
@@ -83,8 +83,13 @@
     return LY_SUCCESS;
 }
 
-static uint8_t
-lyd_hash_table_val_equal(void *val1_p, void *val2_p, uint8_t mod, void *UNUSED(cb_data))
+/**
+ * @brief Compare callback for values in hash table.
+ *
+ * Implementation of ::values_equal_cb.
+ */
+static ly_bool
+lyd_hash_table_val_equal(void *val1_p, void *val2_p, ly_bool mod, void *UNUSED(cb_data))
 {
     struct lyd_node *val1, *val2;
 
@@ -120,7 +125,7 @@
  * @return LY_ERR value.
  */
 static LY_ERR
-lyd_insert_hash_add(struct hash_table *ht, struct lyd_node *node, uint8_t empty_ht)
+lyd_insert_hash_add(struct hash_table *ht, struct lyd_node *node, ly_bool empty_ht)
 {
     uint32_t hash;