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/printer.c b/src/printer.c
index 4b07b8b..def1fa8 100644
--- a/src/printer.c
+++ b/src/printer.c
@@ -71,7 +71,7 @@
     {"unique", "tag", 0},                       /**< LYEXT_SUBSTMT_UNIQUE */
 };
 
-uint8_t
+ly_bool
 ly_is_default(const struct lyd_node *node)
 {
     const struct lysc_node_leaf *leaf;
@@ -109,7 +109,7 @@
     return 1;
 }
 
-uint8_t
+ly_bool
 ly_should_print(const struct lyd_node *node, uint32_t options)
 {
     const struct lyd_node *elem;
@@ -429,7 +429,7 @@
 }
 
 API void
-ly_out_free(struct ly_out *out, void (*clb_arg_destructor)(void *arg), uint8_t destroy)
+ly_out_free(struct ly_out *out, void (*clb_arg_destructor)(void *arg), ly_bool destroy)
 {
     if (!out) {
         return;