Add friends read endpoints

Hey folks,

Guess whose back...back again :tongue:

So this PR is starting to make work on adding friend read endpoints. I've assumed that `friends/userid` would return the friends for a user_id:
![friends](https://cloud.githubusercontent.com/assets/1377956/4770472/4a050746-5b86-11e4-9065-d5bc7a0a4e71.png)
Then I've assumed that `friends/userid/friend/friendid` would essentially be:
![member_friend](https://cloud.githubusercontent.com/assets/1377956/4770516/ba1dd9ae-5b86-11e4-985b-b328707a0cb9.png)

You'll note that I'm not doing any error handling yet and I'm always using `'type' => 'alphabetical'` in these PR's because I've got stale test data locally and I'm purely just trying to get some kind of movement on the BP-API because I figured somethings better than nothing at the moment.

The deeper I get down this rabbit hole the more I want to rework my other PR's but I guess that's how it goes :smile: