Added EventMachine Sinatra Example

When I first implemented this, it took me a while to figure out
how to do it properly. Even though it rides the line between being
an EventMachine example and a Sinatra example, I believe it can
be very useful to other Sinatra users. And more examples can't hurt
right?
Removed /api from dispatch

I had that in there to test it out (for the comments above) but I don't
want that to be in the main example, so I'm removing it. Also, it needs
to be consistent with the curl/ab requests that are/might-be mentioned
in the recipe.
Updated `run` method signature

It would make more sense (practically) for the run method
to take some options on how the server will be run. So...
Now it does!  :-]