* add gameConf.use_image_load_background_thread

* preformance

* fix config not saving

* add gameConf.use_image_scale_multi_thread

* fix default use_image_load_background_thread

* use premake 5.0.0-beta7

* readme

* use premake mac from github release & remove Rosetta thing (#43)

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Co-authored-by: Nanahira <nanahira@momobako.com>