This allows clients to link GLFW with a staticly-built loader library.
This is useful in hermetic build systems that build the Khronos loader
from source, rather than depending on the LunarG SDK binaries.
Closes#820.
Added GLFW_INCLUDE_VULKAN. Added glfwVulkanSupported,
glfwGetRequiredInstanceExtensions, glfwGetInstanceProcAddress,
glfwGetPhysicalDevicePresentationSupport and glfwCreateWindowSurface.
Added port of LunarG SDK tri example.