Initial pass at new style Users Controller 

Initial Controller routes and methods:

- [x] get all users
- [x] get single user
- [x] create user
- [x] update user
- [ ] delete user

Test coverage routes and methods:

- [ ] get all users
- [ ] get single user
- [ ] create user
- [ ] update user
- [ ] delete user
Should this be `slug`? Or is the `slug` the `user_nicename`?