Implement I_AM_THE_DESTROYER
Revert behaviour of calling destroy twice deleting records

As per #92
update README for #92
Support Ruby 2.1.0
Relation doesn't have a default_scoped attr anymore

As of https://github.com/rails/rails/commit/94924dc32baf78f13e289172534c2e71c9c8cade
Tweak test setup to run on activerecord 4.1.0 as well
Remove duplicated ParentModel in test file
Override activerecord destroy!

As of https://github.com/rails/rails/commit/5aab0c053832ded70a3a4b58cb97f8f8bba796ba
that is the method called when destroying associated records.

Example: Both Article and Comment models acts_as_paranoid. Once an
article is destroyed it's expected that all of its comments are
destroyed the same way by only touching the deleted_at column rather
than permanently removing the object from the database.
Run travis build on both rails 4.0 and 4.1
Add test for destroying records in Rails 4.1