Function Request: Add "end-of-file" function in snippet

Hi there,

It would be nice have an operator to say "add this to eof", like

snippet
- name: markdown link reference
- trigger: lref
- text: 

```
    [${1:Title}][${2:ref}]
    ${eof}[${3:ref}]: ${url}
```

Do i explain myself?

If i have time i will try to study the code to add more ideas or even submit a pull request, but right now i don't have too much time, sorry. 
