fixed a bug that raise an error when the uri part of a [[]] tag unintentionally includes another tag at the end
fixed a bug that raises an error when the uri part of a [[]] tag unintentionally includes another tag at the end
When no url follows the optional vertical bar in a link tag, the resulting href attribute becomes empty.

This is the same behaviour as hikidoc, but I am not sure if it is intentionally chosen or not...
merged from github
renamed make_html_element create_self_element
renamed HtmlFormat.create_plain HtmlFormat.get_plain
properly set the lang attribute of <html> element
changed the default encoding of HtmlElement/XhtmlElement.doctype to UTF-8
simplified the definition of HtmElement/XhtmlElement.doctype
add Rakefile to execute unit tests
test_block_head_re_when_commentoutleaf now compares string representations of Regexp instances, instead of the instances themselves.
introduced ELEMENT_TYPE and ELEMENTS_FORMAT to make the assignment to TagFormats clearer
separated the procedure to assign TagFormats into HtmlElement.assign_tagformats
simplified the definition of XhtmlElement class
The intention of the assignment of ELEMENTS_FORMAT in XhtmlElement would become clearer.
just a tidy-up
fixed a bug. XhtmlElement must not share ELEMENTS_FORMAT with HtmlElement.
added a test for empty elements
corrected the shebangs of inlineparser.rb and blockparser.rb
the first commit of plaintextformat.rb