Client functions creates new coroutine an returns Deferred (#26)

* Updates the `Client` functions to return a `Deferred`

The functions inside the client create a new Coroutine, in the IO dispatcher, that async the requests and return a Deferred object.

* Fixes the `ClientTest`

Fixes the test function to handle the `Deferred` wrapper object.

* Fixes the `Dispatchers` in the `RequestHandler`

Replace the `withContext(Dispatchers.IO)` with `coroutineScope`.

Removes some unused imports.

* Update the `README`

* Update the kdoc in the `Client`

Author: MaicolAntali

README.md

@@ -67,11 +67,11 @@ fun main() = runBlocking {
     val client = ClientBuilder("email", "password").build()
 
     // Retrive player info
-    val player = client.getPlayer("#tag")
+    val player = client.getPlayer("#tag").await()
     println("Name: ${player.name}, TH lvl: ${player.townHallLevel}")
 
     // Retrive clan info
-    val clan = client.getClan("#tag")
+    val clan = client.getClan("#tag").await()
     println("Name: ${clan.name}, Tag: ${clan.tag}")
 }
 ```