Go wrapper for Paybook's Sync API

The example in https://github.com/Paybook/lite-go claims to be lightweight but it actually contains a whole web framework (beego) on it, besides requiring bower and node and stuff, this is pretty unusual for a Go library/example and it’s too complex, IMHO.

If you’re also writing a Go service and you want to connect it to Paybook’s Sync API you may want to take a look at https://github.com/mazingstudio/paybook, it’s just a few lines of code + tests and it doesn’t have any odd requisites besides the standard library. We don’t have any user-level docs yet, our main focus is being able to use the sync API, we’ll add proper docs later if we find time for that. Any contributions are welcome!