Add a window class

Nothing fancy yet. Windows can be opened and closed and checked if currently
open. There are static methods for getting a list of all windows and a list
of open windows.

Also adds Premake as a build system.
Add a vector class
Add methods for window positioning
Add methods for window sizing
Fix initial window position and size for hidden windows on X11
Change windows to start closed by default
Fix random freezes when setting the window position on X11