Replace allocator struct with function pointers

lib/include/tree_sitter/api.h

@@ -134,13 +134,6 @@ typedef enum {
   TSQueryErrorLanguage,
 } TSQueryError;
 
-typedef struct {
-  void *(*malloc)(size_t);
-  void *(*calloc)(size_t, size_t);
-  void *(*realloc)(void *, size_t);
-  void (*free)(void *);
-} TSAllocator;
-
 /********************/
 /* Section - Parser */
 /********************/
@@ -148,15 +141,18 @@ typedef struct {
 /**
  * Switch to a new allocator.
  *
- * Returns true iff the switch successes.
- *
- * This function can only be invoked *once*, before tree-sitter has allocated
- * any memory via malloc/calloc/realloc. Otherwise, memory bugs could occur
- * since some memory is allocated by the old allocator, but freed by the new
- * one.
+ * This function can be invoked more than once. However, the application needs
+ * to pay attention to the memory allocated by the old allocator but might be
+ * freed by the new one.
  *
+ * Specifically, the application either,
+ *  1. ensures all parsers and trees are freed before calling it;
+ *  2. provides an allocator that shares its state with the old allocator.
  */
-bool ts_set_allocator(TSAllocator *new_alloc);
+void ts_set_allocator(void *(*new_malloc)(size_t),
+		      void *(*new_calloc)(size_t, size_t),
+		      void *(*new_realloc)(void *, size_t),
+		      void (*new_free)(void *));
 
 /**
  * Create a new parser.