Add filter for custom processors

[Shelob9]

#115

I'm working on my plugin that uses that, will share once I'm more sure it works right and it's pushed to Github so you can see the use case.

[JasonHoffmann]

This is a great extension. A couple of questions though.

• Right now, that filter would only allow adding a single custom processor. Would it be more useful to allow for an array?
• Would it be possible to add a test for the filter? Just checking that the filter is able to register an external class. If not, I can add one
• There are a few code style issues (https://travis-ci.org/reaktivstudios/locomotive/jobs/202697661), but these don't need to addressed until everything is set

Other than that, I'd say this would be a welcome addition

[Shelob9]

• Right now, that filter would only allow adding a single custom processor. Would it be more useful to allow for an array?
  Not sure I follow the concern, this allows any number of custom processors. I updated the readme with an example that adds two custom processors.

• Would it be possible to add a test for the filter? Just checking that the filter is able to register an external class. If not, I can add one

Yes, but I'm kind of out of time on this experiment...

• There are a few code style issues (https://travis-ci.org/reaktivstudios/locomotive/jobs/202697661), but these don't need to addressed until everything is set
  I updated in hopes of passing.

[Faison]

Hi @Shelob9 ,

I noticed that the original plugin code had a bit of repeat code in it and that's something I'm hoping we can start to reduce. So I've made an attempt at this and pushed it up in the branch feature-allow-custom-batch-processors, while also including your filter to allow custom batch processors.

It uses the same filter name, but instead of returning a class name string, you would return your batch processor object already instantiated. Could you checkout that branch and let me know if that change would satisfy your use case?

Thanks,
Faison