Add non-blockin amqp_open_socket - amqp_open_socket_noblock

As discussed in https://github.com/pdezwart/php-amqp/issues/63. I didn't add any ssl support neither integrate in `amqp_open_socket` while I'm not sure it doesn't break anything. Should i use `varargs` to pass `timeout` into `amqp_open_socket_noblock` via `amqp_open_socket` ? Maybe completely replace `amqp_open_socket` code with `amqp_open_socket_noblock` while the last one does both blocking and non-bloking connection?