Refactor HTTP clients: separate admin and client

[mederic-p]

Closes #75

Overview

This PR separates the client and admin HTTP api clients in order to avoid conflicts later when implementing the Admin API.

Changes

• Added HTTPClientAPI and HTTPAdminAPI classes that subclass the base HTTPAPI class.

Implementation Details

This split is necessary to avoid future conflicts. For now if we want to retrieve a user we can use the function:

public static func getCurrent(using client: HTTPClient, callback: @escaping User.RetrieveRequestCallback) -> User.RetrieveRequest? {}

The problem is that this method will be in both client and admin APIs so we need a way to differentiate it.

The new implementation will be:

public static func getCurrent(using client: HTTPClientAPI, callback: @escaping User.RetrieveRequestCallback) -> User.RetrieveRequest? {}

for the client API, and

public static func getCurrent(using client: HTTPAdminAPI, callback: @escaping User.RetrieveRequestCallback) -> User.RetrieveRequest? {}

for the admin API.

Usage

The readme has been updated to reflect the changes. The only difference is the initialization of the client that we now do like this:

let client = HTTPClientAPI(config: config)