Activate snippets on files with extension `.j2`

This library does not recognize that snippets can be inserted in files with the extension `.j2`. Consequently, one can either have `jinja2` syntax highlighting or snippets, but not both. It would be nice if this extension would turn itself on if `.j2` appeared anywhere in the file name.
For example:
```
"mytemplate.txt.j2"
"emails/mytemplate.txt.j2"
"mytemplate.j2.html"
```