Consider using a generic Event

[reillyeon]

The proposed WebIDL for this API includes a SerialConnectionEvent. The TAG design principles suggest using a generic event and storing state in the target attribute. This change would require moving the connect and disconnect event handler attributes to the SerialPort interface and defining that events bubble from SerialPort instances to the singleton Serial instance.

[domenic]

I think this advice isn't as applicable here, because the port is not itself an EventTarget, and thus cannot be the target of the event. A custom event subclass seems very reasonable for this case.

[reillyeon]

This was fixed by #105.