Use the same parameters of dummy asyncore like in
python documentation
Added new option to use poll instead of select in asyncore.loop call

By default asyncore.loop() uses select() and this has some
downsides. Biggest one is a hard fd limit of 1024. When running
bigger apps using waitress there's quite big chance of hitting that.
Using pool() instead of select() removes the limit of 1024 fd.
select() and poll() provide basically the same functionality.
Added use_poll into adjustment tests
Updated docs with new use_poll flag