Add "unreleased" type note
Add "unreleased" note to docs/assets/
Add "unreleased" note to /docs/configuration about kramdown as the new default
Make the icon for the unreleased note brighter
Make the unreleased note type icon dark. Props @cobyism
Add verbiage around installing pre-releases of jekyll.
Shorten header for example of each note type. Props @cobyism
Be a bit more vague about when features are available in pre-releases.
Added docs for installing from master.
Merge pull request #2061 from jekyll/unreleased-features-warnings-on-site

Unreleased features warnings on site
Update history to reflect merge of #2061 [ci skip]