Support a new `relative_include` tag
Trash the subclass
Rename tag to `include_relative`
Add the slugify Liquid filter
Add a test for the slugify Liquid filter
Document the slugify Liquid filter
Remove Good Include

The plugin is deprecated.
Merge pull request #2880 from kansaichris/slugify-liquid-filter
Update history to reflect merge of #2880 [ci skip]
Merge pull request #2881 from penibelst/patch-1
Update history to reflect merge of #2881 [ci skip]
Define methods for shared vars between include & include_relative
Separate include_relative test out into its own context
Test that includes relative to self are included
Add tests around nasty include attempts
Add documentation on the include_relative tag
Rename method to `resolved_includes_dir`
Sanitize the resolved includes path
Merge pull request #2870 from gjtorikian/support-relative-include
Update history to reflect merge of #2870 [ci skip]