Add a feature similar to the old ?debug= parameter [RD-22]

I merged #53 into this just to make testing easier, but I can remove that dependency if desired.

As discussed in the ticket, this is activated by appending '+' to the end of a redirect url. We don't have exactly the same structure as the old code, so the two won't be verbatim. They should be roughly equivalent, though.

All tests pass.