Test that emojis are wrapped in Span

```
% pandoc -f commonmark+emoji -t native
My:thumbsup:emoji:heart:
^D
[Para [Str "My",Span ("",["emoji"],[("data-emoji","thumbsup")]) [Str "\128077"],Str "emoji",Span ("",["emoji"],[("data-emoji","heart")]) [Str "\10084\65039"]]]
```

```
% pandoc -f markdown+emoji -t native
My:thumbsup:emoji:heart:
^D
[Para [Str "My",Span ("",["emoji"],[("data-emoji","thumbsup")]) [Str "\128077"],Str "emoji",Span ("",["emoji"],[("data-emoji","heart")]) [Str "\10084\65039"]]]
```

```
% pandoc -f commonmark+emoji -t html
:zero: header
=============
My:thumbsup:emoji:heart:x :hearts: xyz
^D
<h1><span class="emoji" data-emoji="zero">0️⃣</span> header</h1>
<p>My<span class="emoji" data-emoji="thumbsup">👍</span>emoji<span class="emoji" data-emoji="heart">❤️</span>x <span class="emoji" data-emoji="hearts">♥️</span> xyz</p>
```