Added enqueue_with_response

[kke]

New method enqueue_with_response for RPC kind of functionality:

job "concat" do |args|
   args['a'] + args['b']
end

Stalker.enqueue_with_response "concat", :a => 'foo', :b => 'bar'
 => "foobar"

I dont' see how it could be tested in single thread.