Add jekyll-thumbnail-filter to plugins list
Use relative path for `path` Liquid variable in Documents
Keep backwards compatibility

Re-add `relative_path` Liquid variable too keep compatibility
Allow Enumerables to be used with "where" filter.
where filter - test return value when filtering a Hash
Utils.slugify: Don't create new objects when gsubbing
Docs: Clarify behavior of 'categories' in permalinks
 Hash#each_key instead of Hash#keys.each. Faster code.
Merge pull request #3017 from glaucocustodio/master
Update history to reflect merge of #3017 [ci skip]
Merge pull request #3011 from fhemberger/master
Update history to reflect merge of #3011 [ci skip]
Merge pull request #2986 from tamagokun/where_filters_enumerable
Update history to reflect merge of #2986 [ci skip]
Merge pull request #2997 from jekyll/utils-slugify
Update history to reflect merge of #2997 [ci skip]
Sort webrick_options
If `--verbose` is given, debug the sh*t out of that.
Turn on FancyIndexing.
Merge pull request #3018 from jekyll/webrick-fancy-indexing