Added new method that allows the creation of an index with settings and also index aliases

The  new method can be used like so:

    type JsonSettings struct {
    	Settings Settings `json:"settings"`
    }

    type Settings struct {
	    NumberOfShards   int `json:"number_of_shards"`
	    NumberOfReplicas int `json:"number_of_replicas"`
    }

    jsonSettings := JsonSettings{}
    jsonSettings.Settings.NumberOfReplicas = 4
    jsonSettings.Settings.NumberOfShards = 3

    res, err := elastigoConnection.CreateIndexWithSettings("mynewindex", jsonSettings)