Added formatters.

	* RBench.formatter = HTMLFormatter
	* All the formatting methods moved to the DefaultFormatter.
Stop bother me with warnings about undefining object_id on Ruby 1.9 please!
RBench.formatter is now an instance, RBench.run can take
formatter as an optional second argument, formatters can
use #setup and #finish_run hooks.

	* RBench.formatter is an instance, so formatter
		can remember state. It can be reused even across
		more RBench.run blocks.
	* You can specify arguments for each formatter which supports
		them, for instance RBench.formatter = YAMLFormatter.new(yaml_file)
	* RBench.run(times, formatter, &block), both times
		and formatter arguments are only optional.
	* Formatters can use #setup and #finish_run hooks.
Added YAML formatter.

It prints results on screen as well as the default
formatter does, but also stores them in a YAML file.
Jeez, undefining #extend is a bloody stupid idea.
Merge pull request #3 from ruby-amqp/master

Formatter + getting rid of these annoying warnings on 1.9