10.Jun.2012
As threatened in the "'Spectrum Play' Error" thread, here's a ruff'n'reddy
interrupt driven full screen wobbling routine which has no practical use
whatsoever apart from making you feel a bit queasy after a while. As a
safety feature it will temporarily de-wobble if the last key pressed was
the ENTER key.

10.Jun.2012
I've added some small refinements (marked in green above) to temporarily
suspend wobbling when the screen is busy. I'll have a think about how to
speed up the intra-wobbling intervals as well.

--

The three lines marked in blue provide some background performance
ehancement while keeping a smooth wobble effect.

