Start adding links to GLU replacements

docs/build.dox

@@ -226,7 +226,8 @@ target_link_libraries(myapp ${OPENGL_glu_LIBRARY})
 @endcode
 
 @note GLU has been deprecated and should not be used in new code, but some
-legacy code requires it.
+legacy code requires it.  See the [section on GLU](@ref moving_glu) in the
+transition guide for suggested replacements.
 
 
 @subsection build_link_cmake_package With CMake and installed GLFW binaries
@@ -269,7 +270,8 @@ target_link_libraries(myapp ${OPENGL_glu_LIBRARY})
 @endcode
 
 @note GLU has been deprecated and should not be used in new code, but some
-legacy code requires it.
+legacy code requires it.  See the [section on GLU](@ref moving_glu) in the
+transition guide for suggested replacements.
 
 
 @subsection build_link_pkgconfig With makefiles and pkg-config on Unix
@@ -313,7 +315,8 @@ cc `pkg-config --cflags glfw3 glu` -o myprog myprog.c `pkg-config --libs glfw3 g
 @endcode
 
 @note GLU has been deprecated and should not be used in new code, but some
-legacy code requires it.
+legacy code requires it.  See the [section on GLU](@ref moving_glu) in the
+transition guide for suggested replacements.
 
 If you are using the static version of the GLFW library, make sure you don't
 link statically against GLU.

docs/moving.dox

@@ -447,6 +447,13 @@ defining @ref GLFW_INCLUDE_GLU before the inclusion of the GLFW header.
 #include <GLFW/glfw3.h>
 @endcode
 
+There are many libraries that offer replacements for the functionality offered
+by GLU.  For the matrix helper functions, see math libraries like
+[GLM](https://github.com/g-truc/glm) (for C++),
+[linmath.h](https://github.com/datenwolf/linmath.h) (for C) and others.  For the
+tessellation functions, see for example
+[libtess2](https://github.com/memononen/libtess2).
+
 
 @section moving_tables Name change tables