Attachment Command

TODO

Fails meaningfully if there was no attachment

Given there is resource at /hello
When following fixture is executed:
<rest:request>
	<rest:get>/hello</rest:get>
	<rest:attachment>hello.txt</rest:attachment>
</rest:request>		
		
Then it should produce following output:
/hello hello.txt (no attachment)

Response body is saved in file and linked from spec

Given there is resource at /hello
Hello World!
When following fixture is executed:
<rest:request>
	<rest:get>/hello</rest:get>
	<rest:attachment>hello.txt</rest:attachment>
</rest:request>		
		
Then it should produce following output:
/hello hello.txt
And there should be file /hello.txt with content
Hello World!