New API to create customer without subscription. See https://apidocs.chargebee.com/docs/api/customers#create_a_customer
New API to fetch invoices for a customer. This helps you fetch the invoices created due to multiple subscriptions present for any customer. See https://apidocs.chargebee.com/docs/api/invoices#list_invoices_for_a_customer
PORTAL as event source added to indicate any changes initiated via Customer Portal.
Customer id reference is added to the invoice attributes.