Wrap source code in code tags

[johnW-ret]

Referencing this issue on markdown-colorcode, this package overwrites some of the behavior used in Markdig that appears to be in line with the CommonMark spec, that is, this package does not wrap code using a code element. Additionally, if a language is present, the spec specifies a class="language-[lang]" attribute as well.

I have not started a fork because I am not sure whether this would be a breaking change or not, however, the general change seems rather simple, adding the following methods to HtmlClassFormatter and then wrapping the inner text in WriteHeader and WriteFooter.

private void WriteHeaderCodeStart(ILanguage language)
{
    WriteElementStart("code", language.CssClassName);
}

private void WriteHeaderCodeEnd()
{
    WriteElementEnd("code");
}

In my case, this would make it easier to enforce consistent styling across my app.