Removed tautological test.
Consume WM_ERASEBKGND.
Added GLFW_AUTO_ICONIFY.

By default, full screen windows that lose focus will be iconified and
the video mode will be restored.  This makes it impossible to create
applications spanning multiple monitors.  The GLFW_AUTO_ICONIFY window
hint will allow users to disable this behavior.

Fixes #143.
Added GLFW_DONT_CARE.

This changes the behavior of framebuffer hints set to zero.  Before,
zero meant that any value was acceptable.  This changes zero to be an
explicit preference and adds GLFW_DONT_CARE to mean that any value is
equally acceptable.

Fixes #70.
Added GLFW_DOUBLEBUFFER.
Added GLFW_FLOATING.

Fixes #23.
Added position testing to windows test.
Made windows test show all windows at once.
Updated glad.
Fixed plural forms on key/button arrays.