Add supported exchange types to the specification

[gomete]

To cover #73

Use example:

channelItem.Bindings = new ChannelBindings 
{
    Amqp = new AmqpChannelBinding
    {
        Is = AmqpChannelBindingIs.RoutingKey,
        Exchange = new AmqpChannelBindingExchange
        {
            Name = "anyName",
            Type = AmqpChannelBindingExchangeType.Fanout,
            Durable = true,
            AutoDelete = false,
            VirtualHost = "anyVirtualHost",
        },
    },
};