Textile heading h-align mark support
https://github.com/redmine/redmine/blob/e575b7a6fcbffd5e48475b735cfc948ed3cc0d0e/lib/redmine/wiki_formatting/textile/formatter.rb#L60
https://github.com/redmine/redmine/blob/e575b7a6fcbffd5e48475b735cfc948ed3cc0d0e/lib/redmine/wiki_formatting/textile/redcloth3.rb#L340
- #4 Sections with ident mark