ClassedHTMLGenerator generates Empty <span></span> tags.

[uwearzt]

See output of ClassedHTMLGenerator example.

[uwearzt]

part of output from examples/synhtml-css-classes.rs (formatted):

...
      <span class="meta group rust">
        <span class="string quoted double rust">
          <span class="punctuation definition string begin rust">&quot;</span>Hello World!<span class="punctuation definition string end rust">&quot;</span>
        </span>
        <span class="meta group rust"></span>
      </span>
      <span class="meta group rust">
        <span class="punctuation section group end rust">)</span>
      </span>
...

that leads to:

1. larger file sizes in html
2. warning i.e. from Firefox developer tools

[uwearzt]

Thanks for the merge 👍