Replaced the GLFW_SHOULD_CLOSE window parameter with the
glfwWindowShouldClose and glfwSetWindowShouldClose functions, allowing
the setting of the close flag from any point in the program.
Having one way to retrieve the cursor position and another (more
verbose) way to retrieve the monitor position is inconsistent. Having
them both work the same way is the least surprising thing.
The expected glfwGetMonitorSize function gets an added Physical in its
name so users won't confuse it with glfwGetVideoMode.
