Implement HttpDeleteWithBody.

The Apache commons folks seemed to leave out the ability for HTTP delete
requests to include a body. Since this is essential to a pretty crucial
chunk of Stripe's API, that just won't do. We build out our own version
of HttpDelete that supports a request body.
Construct delete requests with a param list.
Merge pull request #16 from anchortab/delete-on-steroids

Delete on steroids.