#User
(CRUD)
##get all users
GET /users
returns [User]
permissions > Student
##get all courses
GET /users/:user/courses
returns [Course]
permissions > Student || if user==:user then Student
##get all problem sets in course
GET /users/:user/:course/sets
returns [ProblemSet] or [UserSet]
##get/update a problem set in a course
GET /users/:user/:course/:set
returns ProblemSet or UserSet
POST /users/:user/:course/:set
returns Success/Failure
##add(assign)/remove problem set
PUT /users/:user/:course/:set
returns Success/Failure
DELETE /users/:user/:course/:set
returns Success/Failure
##get grade for a set
GET /users/:user/:course/:set/grade
returns a Grade (or a number)