idevicescreenshot: Allow user-specified output filename
idevicescreenshot: Allow user-specified output filename

Signed-off-by: Martin Szulecki <048d26ae6dd09f6cf74dabd757723ee3f57a7675@libimobiledevice.org>

Tatsh/libimobiledevice,Tatsh/libimobiledevice,libimobiledevice-win32/libimobiledevice,upbit/libimobiledevice,kalev/libimobiledevice,libimobiledevice-win32/libimobiledevice,Tatsh/libimobiledevice,upbit/libimobiledevice,libimobiledevice-win32/libimobiledevice,libimobiledevice/libimobiledevice,patweb/libimobiledevice,upbit/libimobiledevice,patweb/libimobiledevice,libimobiledevice/libimobiledevice,kalev/libimobiledevice,kalev/libimobiledevice,patweb/libimobiledevice,libimobiledevice-win32/libimobiledevice,Tatsh/libimobiledevice