* new option `upload_achievements_icons_to_gpu` in `configs.main.ini` which controls whether the overlay should upload the achievements icons to the GPU and display them or not
* synchronize overlay proc with the periodic steam callback in a better way to avoid FPS drop
* prevent overlay flickering regression
* upload achievements icons to the GPU in the overlay proc periodically, this dramatically decreased the startup locking/halt time
* fix a potential deadlock scenario in the overlay as a result of synchonizing with 2 mutex objects
* make sure buffer is null terminated in `Steam_UGC::GetQueryUGCPreviewURL()`
* implement 2 new useless ugc stuff + use an already made function to check for handle validity
* allow showing the progress indicator in the achievement notifications, not only in the achievements list
* don't play sound when showing progress notifications
* disable progress notifications if the setting in the .ini was set
* convert the animation duration to millisec once during settings parsing
* decrease the notification margin from 10.0 to 5.0, it looked way shifted on larger screens
* pass around instances on std::chrono instead of float, use float in the final stage when processing/operating-on the time (if needed)
* decrease the animation duration to 0.35 sec, looks more swishy!
* added a new button to the overlay `"Test achievement"` which triggeres a test achievement
* added a new overlay appearance option `Achievement_Unlock_Datetime_Format` which allows changing the date/time format of the unlocked achievements
* removed the condition which disabled the overlay sounds when it is shown
* fix a mistake when mixing output from generate_emu_config tool
* ensure output from generate_emu_config tool is written as soon as possible in case another stage threw an exception
* fix a bug when writing .ini, ensure everything is a string
* new readme for the migration tool
* changed the environment variable `SteamAppPath` to `GseAppPath`
* allow loading `config.ini` from global settings path + merge it with the local one, and allow the local one to override the global one
* fixed the path returned by `get_user_appdata_path()` to include the path separator
* updated readmes
