alt attribute should contain the Unicode emoji

The `alt` attribute _should_ contain the Unicode emoji and only that, the current descriptive text _may_ be used in the `title` attribute.

```` html
🦖
````

currently yields

```` html

````

but should result in

```` html

````

I noticed this problem when trying to copy and paste rendered comments where I did not get the emoji as expected even though the other environment supported emojis.