option for JSON format export and ability to pass through additional data objects

[mattscotty]

Hi, I've added two pieces of functionality into this plugin that I'd like to contribute as i liked this plugin when using it.

the first is the ability to export to a JSON format rather than a CSV of ID's (optional)

the second is the ability to pass through custom data objects that will be exported as part of the JSON, for example an additional ID or email address.

Let me know your comments. Thanks.

[mellodev]

thx for this, I used some of your code

[neoascetic]

This is a must-have IMO