Merge branch 'develop' into 2html
delete a duplicated tagname in Html5Tags
add Xhtml5Element
introduced @generator=HtmlElement in class HtmlFormat
removed the redefinition of XhtmlElement#create_element
removed the redefinition of XhtmlElement#visited_result
introduced HtmlFormat.setup_new_formatter
added class Xhtml5Format
refactoring of HeadingNodeFormatter#create_self_element
modified HtmlElement#add_end_comment_for_div and and renamed to add_end_comment_for_div_or_section to reflect the modification
added a test for Xhtml5Format
added class Xhtml5Template
split the initialization of @base into a function
attributes of an element can be passed as a parameter of HtmlElement#intialize()
attributes of an element can be passed as a parameter of HtmlElement#intialize()
a refactoring of HtmlTemplate#set_path_to_base()
defined HtmlTemplate#create_element
create elements using create_element
make HtmlTemplate#set_path_to_base() private
passed an attribute of @html as a parameter