Data-dev support for loops

[MiniXC]

Just add the key to the already existing data-dev string.

Example

To access the first item in the items array, frix should generate a data-dev string of a b 0 c instead of the current a b c.

{
  "a": {
    "b": {
      "items": [{
        "type": "c",
        "data": {
          // ..
        }
      }]
    }
  }
}

[bminixhofer]

This is not 100% tested. Please test with real data and report back.

[MiniXC]

Loops + data-dev cause everything to essentially time out... The following test made all the other tests with the same frix instance go red too.

  it('should respect dev flag in loops', function(done) {
    let expectedHtml = noWhitespace(`
      <article class="article">
        <header class="header">
          <h1 class="heading" data-dev="0 header heading-en" data-dev-targets="text-content">Tree</h1>
          <h1 class="heading" data-dev="0 header heading-de" data-dev-targets="text-content">Baum</h1>
          <p class="author">written by <a href="https://simple.wikipedia.org/wiki/Tree" data-dev="0headerauthor" data-dev-targets="url-href:link text-content:name">Wikipedia</a></p>
        </header>
        <p data-someattribute="something" data-dev="0" data-dev-targets="text-data-someattribute:attribute richtext-content:text">A tree is a tall plant with a trunk and branches made of wood.</p>
      </article>
      <br/>
      <cite class="quote" data-dev="1" data-dev-targets="text-content">Insert smart-ass quote here.</cite>
      <br/>
    `);
    let app = express();
    opt.key = 'loop-test.json';
    frix.render({dev: true}).then((requestHandler) => {
      app.use(requestHandler);
      chai.request(app).get('/loop-test').end((_, res) => {
        expect(noWhitespace(res.text)).to.equal(expectedHtml);
        done();
      });
    });

    after(function() {
      opt.key = 'key.json';
    });
  });