- Add vsync flag to t.window and lovr.graphics.createWindow.
- vsync is 1 by default.
- Some headset drivers override vsync if they have special timing requirements.
I'm not sure why this was changed. It doesn't make very much sense
because setWindow can't be called multiple times, and it can't be
called with nil/NULL.
Platforms that want to use glfw for most of their platform code can
include "glfw.h" for common functions, in a single-file-lib fashion.
All glfw code is in this file.