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>
```
