Add the system call outputDebugString.

This doesn't do anything on retail consoles, but homebrew developers can use it to debug applications in Citra or in other 3DS emulators which HLE this system call.

Addresses #9.

My implementation works with what we have in Citra (i.e. I can call this in a homebrew application and the string is printed when running it in Citra), but actually I really have no idea what I've done there...