Add TSAllocator and ts_set_allocator in api.h

lib/include/tree_sitter/api.h

@@ -134,10 +134,31 @@ 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 */
 /********************/
 
+
+/**
+ * The allocator.
+ */
+extern TSAllocator *ts_allocator;
+
+/**
+ * Switch to a new allocator.
+ *
+ * Returns the old allocator. The caller needs to take care of any allocated
+ * memory managed by the old allocator.
+ */
+TSAllocator *ts_set_allocator(TSAllocator *new_alloc);
+
 /**
  * Create a new parser.
  */