Install will_paginate

This gem is used to restrict the amount of data that is returned with one request.
Add default page size to User model

The default page size for users is 25, but can easily be changed by overwriting this parameter.
Make UsersController's output dynamic

Until now, the controller render only static pages. With this addition, it shows the actual users.
Add JSON views for UsersController

The #index and #show action have been extended to feature a JSON view.
Throw error when accessing non-existing users

When requesting html, an error is displayed when a user does not exist. When requesting json, an error code of 404 is returned.
UsersController responds to JSON

The UsersController API returns JSON, so it has been added to the respond_to formats. Additionally, doorkeeper has been configured to intercept JSON requests and enforce a valid authentication token.
Disable authentication for JSON API

To enable easy testing of the API, the authentication is disabled per default. Users should enable them when they need the privacy.
Merge branch 'feature/user-api' into develop
Update README file
Merge branch 'release/0.2.0' into develop