Added support for topic based exchanges and multiple consumers

[mikery]

I needed to use topic-based exchanges, so I removed the hard-coded 'type="direct"' exchange declarations. It will default to "direct" if no exchange_type is specified.

I also added an examples dir with a file showing how to use a topic-based exchange with txamqp to help people get up and running quickly.

[pfreixes]

Not just you should give type argument, all params behind exchange declare must be give