Add PPSSPP package, an emulator for PSP.
Just a reminder to the maintainers that PPSSPP is one of those emulators that are very actively developed and providing stable builds in the repo isn't desired as pretty much everybody wants to use nightlies. The "stable" tag doesn't mean much in such cases. It's kind of similar to WINE - nobody in their right mind would choose stable over dev or wine-staging. Would it be feasible to provide ppsspp builds compiled straight from the master?