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_free.c b/src/tree_data_free.c
index 7c0a52a..176d39f 100644
--- a/src/tree_data_free.c
+++ b/src/tree_data_free.c
@@ -23,7 +23,7 @@
 #include "plugins_types.h"
 
 static void
-lyd_free_meta(struct lyd_meta *meta, uint8_t siblings)
+lyd_free_meta(struct lyd_meta *meta, ly_bool siblings)
 {
     struct lyd_meta *iter;
 
@@ -77,7 +77,7 @@
 }
 
 static void
-ly_free_attr(const struct ly_ctx *ctx, struct lyd_attr *attr, uint8_t siblings)
+ly_free_attr(const struct ly_ctx *ctx, struct lyd_attr *attr, ly_bool siblings)
 {
     struct lyd_attr *iter;
     LY_ARRAY_COUNT_TYPE u;
@@ -157,7 +157,7 @@
  * @param[in] top Recursion flag to unlink the root of the subtree being freed.
  */
 static void
-lyd_free_subtree(struct lyd_node *node, uint8_t top)
+lyd_free_subtree(struct lyd_node *node, ly_bool top)
 {
     struct lyd_node *iter, *next;
     struct lyd_node *children;
@@ -222,7 +222,7 @@
 }
 
 static void
-lyd_free_(struct lyd_node *node, uint8_t top)
+lyd_free_(struct lyd_node *node, ly_bool top)
 {
     struct lyd_node *iter, *next;