Doxygen API Documentation

The purpose of this is to get some API documentation out there for people to use.  (See issue #1)

I've chosen Doxygen as a tool to generate it based on comments in the header file.  Hopefully this will encourage the documentation to be updated as the API changes in the future.

Current output can be found [here](http://alanxz.github.com/rabbitmq-c/docs/0.2/)

The first cut of this is pretty rough and there's a number of key areas this needs to be improved upon:
* Provide a mainpage so when people land in the documentation they have a place to get started for those who are unfamiliar with rabbitmq or AMQP
* Link in examples/create examples that exercise the API in common ways
 * ```amqp_table_t``` manipulation
 * Using the url decoder thing
* Link in the man pages for the tools
* Provide a getting started guide (probably want to link to the rabbitmq getting started page for common patterns: http://www.rabbitmq.com/getstarted.html)
* Decide what APIs really should be deprecated