I'm not entirely sure this whole list is necessary. For instance, in the FontAwesome stylesheet, I see the following declaration:

```
.fa-sort-up:before,
.fa-sort-asc:before {
  content: "\f0de";
}
```

Yet you have it mapped below as:

```
'sort-up' => 'sort-desc'
```

Isn't it already mapped?

For names that we do need to remap, I think we should do it in the stylesheet (output by the HTML5 converter). Perhaps we can have an asciidoctor-font-awesome-compat.css that we either link to or embed depending on the linkcss setting (just like we do with the CodeRay stylesheet).