Added API functions for modulating the colour and alpha of a texture

include/GameEngine.h

@@ -74,6 +74,8 @@ void clip_render_rects_to_drawing_area(RenderRect *src, RenderRect *dest);
 
 RenderRect get_texture_asset_rect(AssetID id);
 void render_texture_asset(AssetID id, RenderRect *src, RenderRect *dest);
+void modulate_texture_color(AssetID id, SDL_Color color);
+void modulate_texture_alpha(AssetID id, u8 alpha);
 TextSize get_text_size_from_font_asset(AssetID id, const char *text);
 void render_text_with_font_asset(AssetID id, const char *text, f32 x, f32 y,
                                  SDL_Color color);