Add, and update, documentation build targets.

doc/build.jam

@@ -0,0 +1,15 @@
+# Copyright (c) 2016 Rene Rivera
+#
+# 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)
+
+###############################################################################
+alias boostdoc
+    : xml/bbref.xml
+    :
+    :
+    : ;
+explicit boostdoc ;
+alias boostrelease ;
+explicit boostrelease ;