Fixed: Completely fails to compile when SDL_GetSystemRAM() and SDL_HasAVX()
       are missing on SDL 2.0.1 and 2.0.2 respectively.

Signed-off-by: Jacky Boen <aqiank@gmail.com>
Added SDL2 packages installation command for Ubuntu (and a few tweaks) in README

Signed-off-by: Jacky Boen <aqiank@gmail.com>
go fmt
synced with upstream