Exit event

[jcristovao]

When redis is not installed, no event is called (namely close). Hence, this PR adds the exiting and exit events, which pass the exitCode and allow the developer to identify if there was a problem launching redis.

Also, when calling closing, pass the result.err to allow the user code to identify any possible error when parsing the configuration.

What do you think?
Thanks

[coveralls]

Coverage decreased (-1.7%) to 98.347% when pulling 8cc2435 on Optylon:exitEvent into d5d04e0 on BrandonZacharie:develop.

[BrandonZacharie]

I see the need you have here and thanks for taking the time to find out what's going on. I agree that it's troublesome to see what went wrong without a hook that provides some information. However, having multiple events that could fire when the library returns control shifts burden to consumers. Rather than adding exiting and exit events, I propose the addition of an error event with which you would get an Error object as expected.

[BrandonZacharie]

An error event would also help resolve #7 since we could publish an error when logfile or any other incompatible configuration is found.