translated "- var..." syntax into jinja's "{% set... %}" syntax

example:

```
- var foo = 'bar'
```

preprocesses to:

```
{% set foo = 'bar' %}
```

What is strange is even though this gets hoisted up as a code node, the preprocessed output already replaced the 
`#{foo}` variable. In other words with the example above `{% set foo='bar' %}` will go on top, but any line such as `p hello, #{foo}` will be `<p>hello, bar</p>` before even getting to jinja.

Perhaps this is intentional by your design. Either way, this works more closely to the jade syntax.