Update ORM URLs, add ORM extensions.

ORM extensions for:

Hierarchies (ActsAsTree, Ancestry, Closure Tree)
Auditing (ActsAsParanoid, Audited, PaperTrail)
"Social" (AR Reputation System, ActsAsTaggableOn)
Merge pull request #197 from mbrookes/patch-1

Update ORM URLs, add ORM extensions.