Replace glad and the Vulkan SDK with glad2

This removes all dependencies from the GLFW test programs on the Vulkan
SDK.

It also removes support for linking the GLFW shared library (dynamic
library, DLL) against the Vulkan loader static library.

docs/build.dox

@@ -52,7 +52,7 @@ If you are using an OpenGL extension loading library such as
 be included _before_ the GLFW one.
 
 @code
-#include <glad/glad.h>
+#include <glad/gl.h>
 #include <GLFW/glfw3.h>
 @endcode
 
@@ -62,7 +62,7 @@ prevent the GLFW header from including the OpenGL header.
 @code
 #define GLFW_INCLUDE_NONE
 #include <GLFW/glfw3.h>
-#include <glad/glad.h>
+#include <glad/gl.h>
 @endcode
 
 

docs/compile.dox

@@ -224,7 +224,7 @@ with the library.
 
 @anchor GLFW_VULKAN_STATIC
 __GLFW_VULKAN_STATIC__ determines whether to use the Vulkan loader linked
-statically into the application.
+directly with the application.
 
 
 @subsubsection compile_options_win32 Windows specific CMake options
@@ -268,7 +268,7 @@ ramps and clipboard.  The options are:
 If you are building GLFW as a shared library / dynamic library / DLL then you
 must also define @b _GLFW_BUILD_DLL.  Otherwise, you must not define it.
 
-If you are linking the Vulkan loader statically into your application then you
+If you are linking the Vulkan loader directly with your application then you
 must also define @b _GLFW_VULKAN_STATIC.  Otherwise, GLFW will attempt to use the
 external version.
 

docs/news.dox

@@ -341,6 +341,20 @@ during compilation of GLFW will still build but it will have no effect and the
 default behaviors will be used.
 
 
+@subsubsection vulkan_sdk_33 LunarG Vulkan SDK dependency
+
+The GLFW test programs that previously depended on the LunarG Vulkan SDK now
+instead uses a Vulkan loader generated by
+[glad2](https://github.com/Dav1dde/glad).  This means the GLFW CMake files no
+longer look for the Vulkan SDK.
+
+Existing CMake projects that depended on the Vulkan SDK cache variables from
+GLFW will need to call `find_package(Vulkan)` themselves.  CMake 3.7 and later
+already comes with a
+[Vulkan find module](https://cmake.org/cmake/help/latest/module/FindVulkan.html)
+similar to the one GLFW previously included.
+
+
 @subsubsection lib_suffix_33 CMake option LIB_SUFFIX
 
 The `LIB_SUFFIX` CMake option has been removed.  GLFW now uses the

docs/quick.dox

@@ -47,11 +47,11 @@ exposes OpenGL 1.2.  The easiest way to work around this is to use an
 If you are using such a library then you should include its header _before_ the
 GLFW header.  This lets it replace the OpenGL header included by GLFW without
 conflicts.  This example uses
-[glad](https://github.com/Dav1dde/glad), but the same rule applies to all such
+[glad2](https://github.com/Dav1dde/glad), but the same rule applies to all such
 libraries.
 
 @code
-#include <glad/glad.h>
+#include <glad/gl.h>
 #include <GLFW/glfw3.h>
 @endcode
 
@@ -177,7 +177,7 @@ a current context to load from.  This example uses
 libraries.
 
 @code
-gladLoadGLLoader((GLADloadproc) glfwGetProcAddress);
+gladLoadGL(glfwGetProcAddress);
 @endcode
 
 

docs/vulkan.dox

@@ -14,10 +14,6 @@ To develop for Vulkan you should download the [LunarG Vulkan
 SDK](https://vulkan.lunarg.com/) for your platform.  Apart from headers and link
 libraries, they also provide the validation layers necessary for development.
 
-The GLFW library does not need the Vulkan SDK to enable support for Vulkan.
-However, any Vulkan-specific test and example programs are built only if the
-CMake files find a Vulkan SDK.
-
 For details on a specific function in this category, see the @ref vulkan.  There
 are also guides for the other areas of the GLFW API.
 
@@ -37,20 +33,14 @@ not need to be linked against the loader.  However, it also means that if you
 are using the static library form of the Vulkan loader GLFW will either fail to
 find it or (worse) use the wrong one.
 
-The @ref GLFW_VULKAN_STATIC CMake option makes GLFW link directly against the
-static library form.  Not linking against the Vulkan loader will then be
-a compile-time error.
+The @ref GLFW_VULKAN_STATIC CMake option makes GLFW call the Vulkan loader
+directly instead of dynamically loading it at runtime.  Not linking against the
+Vulkan loader will then be a compile-time error.
 
 @macos Because the Vulkan loader and ICD are not installed globally on macOS,
 you need to set up the application bundle according to the LunarG SDK
-documentation.  To help the GLFW CMake files find the SDK, you can set the
-`VULKAN_SDK` environment variable to the `macOS` subdirectory of the SDK.
-
-@code{.sh}
-env VULKAN_SDK=/example/path/to/vulkansdk/macOS cmake .
-@endcode
-
-This is explained in more detail in the LunarG Vulkan SDK release notes.
+documentation.  This is explained in more detail in the
+[SDK documentation for macOS](https://vulkan.lunarg.com/doc/sdk/latest/mac/getting_started.html).
 
 
 @section vulkan_include Including the Vulkan and GLFW header files