EventDemultiplexer: add Event bound to the associated type
EventDemultiplexer: add Event bound to the associated type

It worth to indicate that the EventDemultiplexer will produce types which
must implement the Event trait.

Signed-off-by: Tibor Benke <0159c19b1c1721a670d8317ea6ed73d9a838ee77@balabit.com>

ihrwein/correlation