Rails 4 Support

I made some changes to support rails 4, and it appears to working correctly without deprecation warnings, but I could not get the test suite to load (it has some deprecated stuff in there that I'm not familiar with, and it says I don't have Bundler installed even though I do). So this need to be legitimately tested, but it works in my project, so I think it's probably close if not there already. 

I also changed some behavior that may be controversial. The change might be good as an option, actually.  on ln 129 of `core.rb` I changed it to use self.update_column, and as a result the deleted_at columns are reverted to nil, but no active record callbacks take place. This is the behavior I needed in my project, and it may be the correct behavior in general, but I'm not sure. Like I said, it could also be an option like `:recover_with_callbacks` or something like that.