added HtmlElement#traverse()
Merge branch 'traverse-htmlelements' into ME-task-specific
Merge branch 'traverse-htmlelements' into converter
set the title attribute of each <a> elements under toc
refactoring of HtmlElement#traverse()
Merge branch 'traverse-htmlelements' into converter
refactoring of create_table_contents()
Merge branch 'converter' into ME-task-specific