Implement `Create` functionality

[matryer]

• Should be able to do changeInfo, Err := session.At("people").Create(resource)

Things to note:

• What happens when you try to Create a resource that already has an ID? Does it just update it, or is the Create method strict?

[tylerstillwater]

We can discuss a strict mode later. Right now if the ID exists in the resource and on the server, it will simply replace it as it is a POST.