Use Alt Key for Shorcuts and New Shorcut for Save/Load Custom Save States

[eldexterr]

Like all others RA emulators when you press Alt + R to open the RetroAchievements Tab or Alt + R + M to open the Memory Inspector

Also Create a shorcut for Saving/Load Custom States like the other emulators, as a developer I need to Save and Load a ton of states so will be very useful to just press for example Ctrl + S, to save a state or Ctrl + L to load one

[Jamiras]

Alt "shortcuts" are actually accelerators for navigating the menu. I'm not sure why the accelerators aren't working - I assume it's something we have to enable in SDL.

Having explicit shortcuts for saving/loading custom states will be handled by #364