add proper capturing of exceptions

[benedikt-budig]

The package is still missing proper capturing of exceptions. The process_response hook in Falcon's middlewares does not contain information on raised exceptions (except for the boolean req_succeeded flag).

A solution could be to add a custom error handler like this:

application.add_error_handler(Exception, capture_all_errors)

and call client.capture_exception(handled=False) inside that handler.