Jinja guidelines

A first (and still somewhat incomplete) version of code guidelines for jinja2 templates.
Please, chip in.
Kann man da das [Whitespace Control](http://jinja.pocoo.org/docs/templates/#whitespace-control) nutzen (und hier mit aufnehmen)?:

```html+Django
{% for item in seq -%}
    {{ item }}
{%- endfor %}
```
Laut Jinja Docs:
> This will yield all elements without whitespace between them. If seq was a list of numbers from 1 to 9 the output would be 123456789.