Add nanoc 4 upgrade guide (WIP)
List removed features
Add more content to upgrade guide
Describe identifiers and globs, and move sections around
Reword About page (WIP)
Improve "why nanoc" section
Add programmability paragraph
Do not run the About page through ERB
Reword SSG paragraph slightly
Fix typo
Tweak wording of About page
Fix wording of Similar projects section
Fix footer links in about section
Merge pull request #45 from nanoc/reword-about-page

Reword About page
DRY up sudo gem note
Highlight active nav section
Move "active" class onto li
Fix home styling
Style subsections as well
Remove nav_title