Added a database schema

David,

I did an initial stab at a schema.  I think that the API objects that return will just be the data presented in the schema. 

So when we say in GET /users  that it returns [User], an array of the User objects presented here. 

I think that this is roughly what we talked about on Saturday, however with a NoSQL database, we can have nested schemas and inheritance, which I listed also. Let me know what you think. 

With a better idea of a schema, I'll get back to looking at the API.