Please add pattern to collection filter.

[taoguangc]

I found that view_filters supports pattern, but filter does not. Can filter also support pattern?
ex:

collections:
  - name: 'blog'
    label: 'Blog'
    folder: 'content/blog'
    ...
    filter: 
      field: 'body'
      pattern: '\S+'
    fields:
      ...
    view_filters:
      - label: 'Post date'
        field: 'date'
        pattern: '\S+'

When I use the pattern in view_filters, it works, but it doesn't work in the filter.