doxygen: Add Markdown type to file processed by doxygen.

src/tools/doxygen.jam

@@ -100,7 +100,7 @@ rule init ( name ? )
         .doxproc = $(.doxproc:D)/doxproc.py ;
 
         generators.register-composing doxygen.headers-to-doxyfile
-            : H HPP CPP : DOXYFILE ;
+            : H HPP CPP MARKDOWN : DOXYFILE ;
         generators.register-standard doxygen.run
             : DOXYFILE : DOXYGEN_XML_MULTIFILE ;
         generators.register-standard doxygen.xml-dir-to-boostbook

src/tools/types/markdown.jam

@@ -1,4 +1,4 @@
 # Copyright David Abrahams 2004. Distributed under the Boost
 # Software License, Version 1.0. (See accompanying
 # file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
-type MARKDOWN : markdown md ;
+type MARKDOWN : md markdown ;