 code-block, highlight remarks/keywords for code/sql
md.formatCode = function (match, title, block) {
  // convert tag <> to &lt; &gt; tab to 3 space, support marker using ^^^
  block = block.replace(/</g,'&lt;').replace(/\>/g,'&gt;')
  block = block.replace(/\t/g,'   ').replace(/\^\^\^(.+?)\^\^\^/g, '<mark>$1</mark>')
  
  // highlight comment and keyword based on title := none | sql | code
  if (title.toLowerCase(title) == 'sql') {
    block = block.replace(/^\-\-(.*)/gm,'<rem>--$1</rem>').replace(/\s\-\-