Users API

# Adding the Users API

Basic CRUD endpoints for users. I decided to leave out _destroy_ for now.

## Standard Endpoints

* `GET /user` - returns the current user's info
* `GET /users/[:id]' - same as above, 401 when id isn't current user
* `PATCH /users/[:id]' - update info, 401 when id isn't current user

## Trusted Endpoints

* `GET /users` - all users (paging to be handled in a future PR)
* `GET /users/[:id]` - get single user info
* `POST /users` - create a new user
* `PATCH /users/[:id]` - update a user