function escapeHTML( text ) {
    return text.replace( /&/g, "&amp;" )
               .replace( /</g, "&lt;" )
               .replace( />/g, "&gt;" )
               .replace( /"/g, "&quot;" )
               .replace( /'/g, "&#39;" );
  }
toHTML( markdown, [dialect]  ) -> String
 toHTML( md_tree ) -> String
 - markdown (String): markdown string to parse
 - md_tree (Markdown.JsonML): parsed markdown tree

 Take markdown (either as a string or as a JsonML tree) and run it through
 [[toHTMLTree]] then turn it into a well-formated HTML fragment.