Modify thin example to use thin-attach_socket + EventMachine-LE

Also update the docs to point at those instead of our thin/EM patches.

With EventMachine-LE's support for attach_socket and Conrad's thin-attach_socket gem, we don't actually need patches to either Thin or EventMachine anymore.

It's possible we should still refer to our patches for posterity (though I'm inclined to say we shouldn't - they're distracting and discouraging), but I'm pretty sure our examples should work out-of-box with published upstream releases of gems, since that's a thing we have the capability to do now.

@nelhage, thoughts?