Added GLFW_ACCELERATION window hint for hardware acceleration

[SuperSodaSea]

• Add GLFW_ACCELERATION window hint to specify whether hardware acceleration is preferred or not. Default to GLFW_TRUE, only available on WGL currently.
• Add GLFW_ACCELERATION window attribute to retrieve whether hardware acceleration is enabled.
• Supports creating window when the Microsoft GDI software OpenGL ICD is the only available implementation by default.

> glfwinfo --no-acceleration
...
OpenGL context version string: "1.1.0"
OpenGL context version parsed by GLFW: 1.1.0
OpenGL context renderer string: "GDI Generic"
OpenGL context vendor string: "Microsoft Corporation"
...

Resolves #589.