Added documentation to the interface

It needed it.
Fixed an error in the documentation

getName should return an integer, not a string.
Changed some details in the interface

Gave a reason for the callETEvent method in the documentation.
Changed the meaning of rate -1 slightly.
Updated MockTracker to match Interface changes.
Finally found the problem

Jag har fått SyntaxError hela tiden, utan att förstå vad problemet
varit.
Nu hittade jag felet. Och har lagat det.
Merge remote-tracking branch 'origin/dell_ETinterface' into dell_Server
Moved default_onETEvent out of class

Det var inte en metod, och jag behövde ha tillgång till den utan en self
referens i klassen. En separat funktion passade bättre.
Merge remote-tracking branch 'origin/dell_ETinterface' into dell_Server
import math helps

Especially when you want to use the math package.
Merge remote-tracking branch 'origin/dell_ETinterface' into dell_Server