[doc] Fix long file names in reference by setting qbk section id.

Author: awulkiew

doc/index/make_qbk.py

@@ -3,6 +3,10 @@
 # ===========================================================================
 #  Copyright (c) 2011-2012 Barend Gehrels, Amsterdam, the Netherlands.
 #  Copyright (c) 2011-2013 Adam Wulkiewicz, Lodz, Poland.
+#
+# This file was modified by Oracle on 2020.
+# Modifications copyright (c) 2020, Oracle and/or its affiliates.
+# Contributed and/or modified by Adam Wulkiewicz, on behalf of Oracle
 # 
 #  Use, modification and distribution is subject to the Boost Software License,
 #  Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
@@ -15,6 +19,7 @@
 cmd = cmd + " --xml xml/%s.xml"
 cmd = cmd + " --start_include boost/"
 cmd = cmd + " --output_style alt"
+cmd = cmd + " --alt_max_synopsis_length 59"
 cmd = cmd + " > generated/%s.qbk"
 
 def run_command(command):