* classify and sort the doxygen "related pages"

by tweaking the filename and adding 2 categories:
   Troubleshooting and Advanced
* use the EXCLUDE_SYMBOLS to clean the class list
  (insteaded of a homemade bash script)
* remove the broken "exemple list"
* re-structure the unsupported directory as mentionned in the ML and
  integrate the doc as follow:
  - snippets of the unsupported directory are directly imported from the
    main snippets/CMakefile.txt (no need to duplicate code)
  - add a top level "Unsupported modules" group
  - unsupported modules have to defined their own sub group and nest it
    using \ingroup Unsupported_modules
  - then a pair of //@{ //@} will put everything in the submodule
  - this is just a proposal !

doc/Doxyfile.in

@@ -564,7 +564,9 @@ WARN_LOGFILE           =
 
 INPUT                  = "${Eigen_SOURCE_DIR}/Eigen" \
                          "${Eigen_SOURCE_DIR}/doc" \
-                         "${Eigen_BINARY_DIR}/doc"
+                         "${Eigen_BINARY_DIR}/doc" \
+                         "${Eigen_SOURCE_DIR}/unsupported/Eigen" \
+                         "${Eigen_SOURCE_DIR}/unsupported/doc"
 
 # This tag can be used to specify the character encoding of the source files
 # that doxygen parses. Internally doxygen uses the UTF-8 encoding, which is
@@ -618,7 +620,7 @@ EXCLUDE_PATTERNS       = CMake* \
 # wildcard * is used, a substring. Examples: ANamespace, AClass,
 # AClass::ANamespace, ANamespace::*Test
 
-EXCLUDE_SYMBOLS        =
+EXCLUDE_SYMBOLS        = MatrixBase<* MapBase<* RotationBase<* Matrix<*
 
 # The EXAMPLE_PATH tag can be used to specify one or more files or
 # directories that contain example code fragments that are included (see