Destroy transitions when resource id destroy

[btrd]

Fix this issue #14

[seuros]

@btrd , Thank you for your PR.
I have some remarks about this change.
:destroy will load every single instance of the change and destroy them one by one.
If a record has thousands of changes , that could be a very expensive and slow process.
:delete_all will delete all the records with 1 SQL query.

The best approach i can think of now, is to delegate this to the database by have a constraint : on_delete: :cascade on the foreign key.

I still think we can add this feature if we can make it configurable.

[seuros]

The foreign key approach will work only in Relational databases. MongoDB will still need this IFAIK.