added asset loading class, zoom factor, vbo switch, shader version

engine/asset.h

@@ -0,0 +1,18 @@
+#pragma once
+
+class Asset
+{
+public:
+#ifdef __ANDROID__
+    static AAssetManager* m_am;
+    AAsset* m_asset = nullptr;
+#endif
+    std::string m_current_path;
+    FILE* m_fp = nullptr;
+    int m_len = 0;
+    uint8_t* m_data = nullptr;
+    bool open(const char* path);
+    uint8_t* read_all();
+    void close();
+};
+