Merge pull request #2 from habibutsu/master

Ability to pass status code from handlers
More flexibility for error handlers.
Normalizing params for JSON or MsgPack payloads is potentially harmfull.
Nullable validation types and more flexible params fun (ex filter_params).
Validation of 1-tuples.
Passing collected stacktrace to error handler.
Hackish handling of general errors with passed through stacktrace.
Throwing validation errors for 1 and 2 tuples.
Ability to debug requests.