Feature/create client

So when you make a GET request to Canvas you need to have two headers: 
 - Authorization: Bearer ...
 - Accept: text/json

When you make a POST request, you need either two or three
 - Authorization: Bearer ...
 - Content-Type: text/json
 - Accept: text/json (if there's data coming back)

As I recall (although it's possible I'm thinking of a different API), if you're missing the Content-Type or Accept header you'll get some kind of bad request error. Even if not, it's good practice just in case the API ever changes in the future to return, say, XML.