Add entries for Go's constants and variables

Fixes #80.
Update Moment.js documentation (1.6.0)
Update D3.js documentation (3.4.5)
Update PHP documentation (5.5.11)
Update Rails documentation (4.1.0)
Update Python documentation (3.4.0)
Update gem dependencies
Fix Minitest deprecation warning
Add missing require for active_support/cache

https://github.com/rails/rails/pull/14667
Enable tab navigation in the main content area using alt+tab

Fixes #77