Coderay's `coderay_bold_every` can be set to false or to an integer, see [CodeRay's numbering.rb (line 35)](https://github.com/rubychan/coderay/blob/master/lib/coderay/encoders/html/numbering.rb#L35). But because the type is set to Integer in kramdown's [options.rb (line 326)](https://github.com/gettalong/kramdown/blob/master/lib/kramdown/options.rb#L326) it's not possible to set it to false.