Also change the `tester` package slightly to use an exposed `Registers`
array rather adding yet another accessor method to retrieve a register
value. This seems to me more transparent and "obvious" - we aren't trying
to hide the fact that there's just a simple memory store there.
Also unexport the `assertRegisterRange` method which was never intended
to be part of the public API.
soypat
deadprogram
Roger Peppe