Consistently use `time.Sleep`, instead of `runtime.Gosched`, to ensure all
goroutines can make progress. `Gosched` wasn't working in the playground
(ref #149).
Also stop trying to compare operation rates. This was tenuous given e.g. how
short the programs ran for, and with the `Sleep`s we now expect the rates to
be similar anyways.
Its not clear for newbies that using `time.Sleep` internally calls `runtime.Gosched()`
Its better to use it directly, moreover on my machine it shows x175 improvement in speed (7m requests per second vs 40k).
