Delete all related crumbs when object is deleted.

[esbanarango]

This PR fixes the issue #25 by deleting all the related crumbs when the object is deleted.

[JonMidhir]

Accord to discussion on #25 I'm going to delay merging this.

Either way it will need to be resubmitted against the version_0.6.0 branch so that it can be released along with the addition of deletion tracking.

Besides the design decision from the discussion, a second problem may be the direct deletion of Redis keys. I think this will leave artefacts in the datastore. Deletion will need to be done by DataMapper Resource methods so that indexes are removed from lists etc.

Thanks for making a start on it!

[esbanarango]

@JonMidhir Thank you for taking the time to check this PR. I'll go ahead and resubmit it against the version_0.6.0. I also like the idea o making it optional, I'll work on that too. Finally I'll change the way of deletion to pass that responsibility to the DataMapper.

[JonMidhir]

Awesome, I'll look into it tomorrow too to see if I can help out. Deleting multiple crumbs while making sure all traces are removed could be a little tricky.