assignment_tag removed in django 2.0

[l-dfa]

Hi, trying to use Waliki 0.9.dev0 in django 2.0.2

I get the error:

...
Django Version:  2.0.2
Exception type: AttributeError
Exception Value: 'Library' object has no attribute 'assignment_tag'
Exception Location: C:\Dati\Studio\Sviluppi\Unavox\venv\lib\site-packages\waliki\templatetags\waliki_tags.py in <module>, line 173
...

I observe in waliki_tags.py#172 the use of an assignment_tag.

In https://docs.djangoproject.com/en/2.0/releases/1.9/#assignment-tag django staff requests:

... Tags that use assignment_tag should be updated to use simple_tag.

I'm sorry to be too busy to submit a PR. however i hope it would be so simple as replace

@register.assignment_tag

with

@register.simple_tag

And I'm very sorry I couldn't use this app in a my project. I appreciate the capacity to write wiki contents using reStructuredText, a type of format not supported from django-wiki, but issue #146 makes it completely unusable.

Thank you from ldfa