Update Kraken.php

Modified status() to behave like other functions ($data array)

Modified request() to accept optionally POST/GET/DELETE (or other obscure HTTP requests). Defaults to POST.

Added get_subaccounts - Gets all subaccounts
Added get_subaccount - Gets a specific subaccount. Expects an account key
Added create_subaccount - Creates a new subaccount. Expects a name.
Added delete_subaccount - Deletes a subaccount. Expects a subaccount key.