Fix for assign tag not evaluating filters issue

The assign tag currently ignores filters on the value side. For example:
````liquid
{% assign number_of_items = arr | size %}
{{ number_of_items }}
````
Outputs:
````text
[object Object],[object Object],[object Object]...
````

So, I've updated the tagSyntax for assign to grab everything on the right side and then I pass that to Liquid.Variable to sort out.

Also, trailing space was auto-removed on file save.