@dzucconi: Wire up saving an article

This wires it up so that you can save (POST/PUT) articles. There's some odd bootstrapping code necessary to work with HAL here that I'll comment on inline. I haven't written tests for it yet b/c I think it's something that can be extracted into halbone, but I'd rather get this up first.

![image](https://cloud.githubusercontent.com/assets/555859/4499528/c78394c6-4a83-11e4-8230-8ffde6c90a3b.png)
I'm also not completely clear on why in the first example there needs to be the extra GET prior to POSTing?

In general I think it's fine to simplify the code at the expense of more requests. (Interestingly, we do this in a few places in force by initializing ordered sets by key instead of just getting their items directly by the set ID; though the benefits there are definitely more dubious.)