docs(tree): add function docstrings

include/vieter_tree.h

@@ -12,19 +12,37 @@ typedef enum vieter_tree_error {
   vieter_tree_not_present = 2
 } vieter_tree_error;
 
+/*
+ * Allocate and initialize a new red-black binary tree.
+ */
 vieter_tree *vieter_tree_init();
 
+/*
+ * Deallocate a red-black binary tree.
+ */
 void vieter_tree_free(vieter_tree *tree);
 
+/*
+ * Insert a new entry into the tree.
+ */
 vieter_tree_error vieter_tree_insert(vieter_tree *tree, uint64_t key,
                                      void *data);
 
+/*
+ * Look for an entry in the tree.
+ */
 vieter_tree_error vieter_tree_search(void **out, vieter_tree *tree,
                                      uint64_t key);
 
+/*
+ * Remove a given entry from the tree.
+ */
 vieter_tree_error vieter_tree_remove(void **out, vieter_tree *tree,
                                      uint64_t key);
 
+/*
+ * Return how many entries are currently in the tree.
+ */
 uint64_t vieter_tree_size(vieter_tree *tree);
 
 #endif