Have extra 20ms delay after every 16th read entry

Have extra 20ms delay after every 16th read entry

Some times the meter refuses to return all entries as expected, and
just returns some crap instead. This becomes especially notcieable
once the meter has reached the limit of 2000 glucose readings.

Having an extra 20ms delay between readings once every 16th reads
appears to help ensuring all data is read reliably out of the device.

Signed-off-by: Timo Kokkonen <timo.t.kokkonen@iki.fi>