fix: enhance the tokenizer's handing of Unicode (#120)

model.h

@@ -115,7 +115,7 @@ public:
     bool init_from_file(const std::string& file_path, const std::string& prefix = "");
     SDVersion get_sd_version();
     ggml_type get_sd_wtype();
-    bool load_vocab(on_new_token_cb_t on_new_token_cb);
+    std::string load_merges();
     bool load_tensors(on_new_tensor_cb_t on_new_tensor_cb);
     int64_t cal_mem_size(ggml_backend_t backend);
     ~ModelLoader() = default;