Configurable tick resolution

Adds option to specify tick resolution. Since `IoLoopBody` is annotated as private and it made more sense to use a constructor option, I went ahead and changed the API of `IoLoopBody#tick`. There isn't much value in specifying the tick timeout per tick anyway, right?

Also, change the default resolution to 5 ms. I'm not sure about this specific value, perhaps it should be as low as 1 ms? 200 or 1000 tick loops per second should not prove to costly CPU-wise, I suppose. What do you think?