cmRST: Cross-reference cmake-developer.7 manual and cmRST Doxygen

The cmRST implementation and the list of capabilities documented in the
cmake-developer.7 manual must be kept in sync.  Add a note to each file
to reference the other.

Help/manual/cmake-developer.7.rst

@@ -34,6 +34,9 @@ Sphinx-generated html and man pages.
 The command-line help processor supports the following constructs
 defined by reStructuredText, Sphinx, and a CMake extension to Sphinx.
 
+..
+ Note: This list must be kept consistent with the cmRST implementation.
+
 CMake Domain directives
  Directives defined in the `CMake Domain`_ for defining CMake
  documentation objects are printed in command-line help output as

Source/cmRST.h

@@ -16,6 +16,16 @@
 
 #include <cmsys/RegularExpression.hxx>
 
+/** \class cmRST
+ * \brief Perform basic .rst processing for command-line help
+ *
+ * This class implements a subset of reStructuredText and Sphinx
+ * document processing.  It is used to print command-line help.
+ *
+ * If you modify the capabilities of this class, be sure to update
+ * the Help/manual/cmake-developer.7.rst documentation and to update
+ * the Tests/CMakeLib/testRST.(rst|expect) test input and output.
+ */
 class cmRST
 {
 public: