Start on upgrading UI theme guide
Talk about context-targeted style sheets
Add syntax theme upgrade guide
Add example links
Add theme guides to the index
Tiny :lipstick: change
Update title to reference packages too
Add some comments to the examples for clarity
Fix link
Add one more bullet point
Add bit about deprecation cop
Add .overlay to the list
Stylesheets -> Selectors
Change link titles
Use new panel classes
Merge pull request #4214 from atom/upgrading-themes

Upgrading theme guides