Add amqp_login function to specify properties to send to broker

Add an overload to the `amqp_login` function that allows the user to send arbitrary properties to the broker.

This will likely be a separate symbol to maintain API/ABI with existing programs (`amqp_login_with_properties`)

The functionality of the new function would be identical to `amqp_login` in every way, except it would have an additional properties parameter that would allow a user to specify additional properties to be sent to the broker.  These properties would be merged with the other properties that rabbitmq-c already sends.  Properties that conflict with existing properties being sent, will silently be over-riden by those being sent by the library.