v2.3.0

Support curlies with length above 1, for example:

const md = require('markdown-it')();
const markdownItAttrs = require('markdown-it-attrs');

md.use(markdownItAttrs, {
  leftDelimiter: '{{',
  rightDelimiter: '}}'
});

let src = 'asdf *asd*{{.c}}';
let res = md.render(src);
console.log(res);  // <p>asdf <em class="c">asd</em></p>