add multivalue field split and strip function to cb_helpers plugin

[evanwill]

make a Liquid filter that splits value on ; and strips each, returning an array. similar to current array_count_uniq

[evanwill]

Or perhaps just strip_each filter, which can be applied to any array to strip all values (without having to iterate in Liquid)

[evanwill]

Replaces doing stuff like this: {% assign subjects = item.subject | split: ';' %}{% capture clean_subjects %}{% for s in subjects %}{{ s | strip }}{% unless forloop.last %};{% endunless %}{% endfor %}{% endcapture %}{{ clean_subjects | split: ';' | compact | jsonify }}