PlainTextFormat#format returns a String object now.
modified the definition of InlineParser.parse into self.parse. The change allows a subclass of InlineParser to use it as a class method.
introduced TableRowParser
a refactoring of TableLeaf.create
implemented TableLeafFormatter and TableNodeFormatter
introduced TableCellNodeFormatter and redefined TableLeafFormatter
removed TableLeafFormatter
removed unnecessary temporary variables
PlainTextFormat::TableNodeFormatter uses TableCellNode now
removed unused constants and a class
added tools/visitor_template_generator.rb
removed an unnecessary statement for print debug
In Rakefile, test_plaintextformat.rb is added in test task
In PlainTextFormat, the assignment of DescSep has been deleted by mistake