On Windows, cursor colors are determined based on the background
color, and if the background color is gray, the cursor might be
invisible. This change adjust the color so that the cursor should
be visible in any cases.
Closes#1583
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
