IsWindowBeingClosed reports whether the window is being closed by
the user.
SetWindowClosingHandled sets whether the window closing is handled
or not. If the state is true, the window is not closed immediately
by the user and the game can handle the closing state. In this case,
the Update function should return an error in order to end the game.
This change also adds examples/windowclosing.
Closes#1574
Callbacks created by NewCallbackCDecl were never released and then
they are leaked, especially when the window size was changed by
SetWindowSize on Windows.
This change defines new callback ID types with uintptr, and reuse
the callbacks.
Closes#1672
This change adds APIs to enable to use system cursor shapes other
than the default shape (an arrow).
This change doesn't add these cursors since they seem a little
different on macOS from the other platforms.
* GLFW_HRESIZE_CURSOR
* GLFW_VRESIZE_CURSOR
Closes#995
