Postage: add support for recipient variables

[bakura10]

While doing a quick overview of what's new in all the API we support, I realized that Postage support variables per recipient. We only support global variables. (Reference: http://help.postageapp.com/kb/api/send_message)

I suggest:

• Renaming getVariables to getGlobalVariables (as in Mandrill, and because it makes sense)
• Adding a getVariables which take recipient address as first parameter (as in Mandrill).

As this is a BC, we may do it for 2.0 (I don't think it's a big deal to iterate quickly, as SlmMail is really working well, I see no problem at quickly having another major version for such things).

[juriansluiman]

What's the status of this? Hasn't there been a PR which already addresses this feature?

[roelvanduijnhoven]

I'll add as an enhancement! One can look at the Mandrill adapter for inspiration how to implement this.