Add support for Jekyll-specific filters

[epage]

• absolute_url
• markdownify, see Include Markdown in Liquid templates cobalt.rs#342
• sassify
• slugify
• jsonify
• inspect
• where
• group_by
• xml_escape
• uri_escape
• normalize_whitespace
• sort
• sample
• push, pop, shift, unshift
• number_of_words
• array_to_sentence_string
• smartify
• date_to_xmlschema
• date_to_rfc822
• date_to_string
• date_to_longstring

See

• https://jekyllrb.com/docs/templates/
• https://github.com/jekyll/jekyll/tree/master/lib/jekyll/filters.rb
• https://github.com/jekyll/jekyll/tree/master/lib/jekyll/filters
• https://github.com/jekyll/jekyll/blob/master/test/test_filters.rb

[Geobert]

I've encountered prepend, cgi_escape, xml_encode

[Geobert]

I'll take care of slugify soon, need it for my blog