Add serialization and deserialization of job errors

[perrin4869]

As discussed in issue #40, for your consideration :)

[LewisJEllis]

Thanks! At a quick glance it generally looks good, and it seems you've covered your bases on documentation and testing. I'll do a more thorough review tonight.

[AurelienRibon]

This is a much required feature ! Stack traces are completely lost over the network, making debug process a total pain. Please merge this PR if it works fine, the world will thank you :D

[skeggse]

Stack traces are now preserved in the job itself in the job.options.stacktraces Array. I think a more cohesive approach to error serialization that includes both storing this kind of data and publishing is warranted. I like that your solution is pluggable, and would be happy to review a revised PR that also stores the serialized errors in Redis.

[perrin4869]

Hm... been a long time since I worked on this and have lost interest since... Don't have any plans to update it. You can close it if you want

[samuelgoldenbaum]

need to get this up and running - really is needed