Ultisnips %%, and %%v

I get an error trying to use these snippets, for `%%` I get an error itself
```
vim.error: Vim:E117: Unknown function: Filename
```

for `%%v` the snippet expands, but to is produced
```
`!v Filename('', 'title')`
```
(https://github.com/honza/vim-snippets/blob/master/autoload/vim_snippets.vim) has examples of what might be useful