Quick spike on injecting Resource

It's not fully done. A quick idea on how Dependency Injection (DI) works in Go
This will clean up `Rels()` being implemented on all resources.
The ultimate goal is to remove all `Rels()` but only injecting `hypermedia.Relations`

I was planning to build a DI lib, but looks like there's [one decent enough](https://github.com/codegangsta/inject) we could take advantage of