Consume WM_ERASEBKGND.
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.
Added glfwGetKeyName.
Added glfwSetSizeLimits.
Formatting.