Moved WGL context logic into OpenGL module.

src/win32_platform.h

@@ -232,6 +232,12 @@ char* _glfwCreateUTF8FromWideString(const WCHAR* source);
 // Time
 void _glfwInitTimer(void);
 
+// OpenGL support
+int _glfwCreateContext(_GLFWwindow* window,
+                       const _GLFWwndconfig* wndconfig,
+                       const _GLFWfbconfig* fbconfig);
+void _glfwDestroyContext(_GLFWwindow* window);
+
 // Fullscreen support
 void _glfwSetVideoMode(int* width, int* height,
                        int* bpp, int* refreshRate,