way to automatically replace emoji_string with the actual emoji

The :emoji_string: sometimes are not rendered by default in HTML pages except GitHub ofc.
It would be nice to have a switch to add the actual emoji instead of the string.

I have tried to automate this, but was unsuccessful.
```vim
autocmd CompleteDone * call FixEmoji()
function! FixEmoji()
let word = expand('')
" remove colons :
let current_word = word[1:strlen(word)-2]
let acemoji = emoji#for(current_word)
execute "%s/" . word . "/" . acemoji . "/e"
endfunction

```

Start with the CompleteDone autocmd and the FixEmoji() example in the issue, then inspect how emoji#for(current_word) is exposed by the plugin. Determine where a user switch would belong and how replacement should behave in HTML-oriented workflows. Done means the requested opt-in conversion is implemented and covered for the described :emoji_string: case.

Written by the indexing model from the issue text.