Add Jekyll::AutolinkEmail and Jekyll::GitMetadata

Add these plugins to the list of plugins.
Merge pull request #2596 from ivantsepp/add_ivantsepp_plugins
Update history to reflect merge of #2596 [ci skip]
Fix Textile link

Fix broken link to Textile site to point to RedCloth
Fix loads of other broken links
Add ids to history blocks which are useful.
Add slugs to the release sub headers, too!
Merge pull request #2601 from alfredxing/master