Add nanoc 4 upgrade guide (WIP)
List removed features
Add more content to upgrade guide
Describe identifiers and globs, and move sections around
Highlight active nav section
Move "active" class onto li
Fix home styling
Style subsections as well
Remove nav_title
Do not add active indicator to homepage
Remove active indicator from mobile stylesheet
Use separate active home link state icon
Add vertical active indicators to mobile version
Merge pull request #49 from nanoc/highlight-active-nav-section

Highlight active nav section
Make footer small
Fix background styling issue
Add GitHub repository link to footer
Swap discussion group and issue tracker links in footer
Simplify 404 page
Update API documentation