ExceptionHandler

A HttpHandler that delegates to an underlying handler.  In the case of an exception during execution of the underlying HttpHandler dispatch to a different HttpHandler based on the Exception's class.

The order the exception handlers are added is important to handle inheritance.  I noticed some of the JAX-RS exception mappers try to calculate the inheritance depth to handle this.  I don't think it needs to try and be that clever.
Added the attachment and it will now re-throw any unmatched exception/throwable.  I wasn't really sure what to name the attachment key let me know if it needs to change.