Respect Parent Application Error Handlers

When inheriting from a parent application, existing error handlers are
lost.

Rescue all exceptions, walking the ancestor tree (starting from self) to
determine if there is a handler for the raised Exception.

Re-raise exception should it be unknown to the handlers.
Rescue only relevant Exceptions
Merge pull request #10 from adam12/bugfix/respect-parent-app-error-handlers

Respect Parent Application Error Handlers