Initial pass at new style Users Controller 

Initial Controller routes and methods:

- [x] get all users
- [x] get single user
- [x] get me
- [x] create user
- [x] update user
- [x] delete user

Test coverage routes and methods:

- [ ] get all users
- [ ] get single user
- [ ] get current user
- [ ] create user
- [ ] update user
- [x] delete user
To maximize usefulness, let's build a CSV list of all missing required parameters before finally returning the `WP_Error`