Refactoring: Created a response object and made simpler resource classes.

1. A ColorMe\Response\Response object is now returned to easily access data and meta-data.
2. ColorMe\Constants now separate the base API url and the different endpoints.
3. ColorMe\Resource\Resource is now in charge of building the resource URL based on the id/extension schema used by the API.
Added resources.

1. Added resources available through the API.
2. Added a `duration` property in ColorMe\Response\Response (This allows us to know how long the Api call took).
3. Refactored the resource class to throw an exception if a resource can only by accessed by id or without id.
Updated documentation.