SDL_WINDOW_ALLOW_HIGHDPI is now used. On platforms where SDL supports
this flag, the window size units are interpreted as abstract scaled
points rather than raw pixels, and may not match the underlying
framebuffer resolution if the display scaling factor is not 1. The
scaling factor and the effective framebuffer resolution are now
displayed in the options menu to reflect this fact.
In addition, the hidden "fullscreen_desktop_mode" setting has been
removed and the behavior is now always as if the value was "1" (the
default). Exclusive fullscreen with modesetting is not very useful,
and does not work well on some platforms (X11 in particular). That code
is not worth maintaining together with the frankly ridiculous complexity
of dancing around with the DPI scaling shenanigans of various operating
systems.
On platforms that do not support SDL_WINDOW_ALLOW_HIGHDPI, the window
size is assumed to correspond to raw pixels, and an effort is made to
disable the operating system's DPI upscaling mechanism, when possible.
This commit also fixes the Windows manifest, broken by
dc57f78d89 thanks to microshaft's amazing
documentation.
Closes #211
